One day in August 1966, Lea Bondi Jaray, a Jewish Viennese art dealer who had fled to London in 1937 with nothing more than she could carry, wrote a letter to Otto Kallir, the owner of the Galerie St. Etienne in Manhattan, beseeching him for help. She was still trying to reclaim a 1912 painting by Egon Schiele of his mistress, Wally, that she had left behind in Vienna.
The letter, written in German, recounts how a Nazi art dealer named Friedrich Welz had come to her home, where the painting hung, and pressed her to give it to him. It refers to the Belvedere, part of Austria's National Gallery:
''He didn't stop urging me in a very unpleasant way until my husband told me: 'Why don't you give in? We may want to leave already tomorrow, and don't make any difficulties. You know what he can do.' So it first came into the property of Welz.
''When I first took back my gallery in 1946, I asked Welz what happened to my picture, and he told me that it was confiscated with the other pictures and that it was in the Belvedere.''
The letter continues: ''There was nothing to do. I had to go urgently back to London.''
Mrs. Bondi, as she was known, then tells of meeting with an eager collector of Schiele, Dr. Rudolf Leopold:
''Later, Leopold came to London, and we talked about my picture. As I thought he was a nice, decent person, I asked him to pick up my picture from the Belvedere and send it to me immediately. And I promised him that I would make efforts for him to find drawings and other works by Schiele in London. The next thing I heard was that my picture was . . . owned by Dr. Leopold.''
Mrs. Bondi died in the late 1970's without getting back the painting or any compensation for it. ''Portrait of Wally,'' which experts say might be worth as much as $2 million, is on view though Jan. 4 at the Museum of Modern Art, part of ''Egon Schiele: The Leopold Collection.'' It is among some 5,400 works of art, including about 250 by Schiele, amassed over the years by Dr. Leopold, a 72-year-old ophthalmologist, self-styled art historian and conservator and, most recently, director for life of a Government-financed foundation that bought his holdings in 1994 and is building a museum in Vienna enshrining his achievement.
''Wally'' is not the only Leopold Collection painting in the Modern's show with a troubled past. At least three additional works also slipped from the grasp of people forced to flee the Nazis. Other paintings have gone through restorations at the hands of Dr. Leopold that some experts fear are intrusive or damaging.
Indeed, the presentation of the Leopold Collection at the Modern -- and previously at institutions in London; Tubingen, Hamburg and Dusseldorf, Germany; Zurich, and Tokyo -- raises serious issues for museums that show individuals' collections: What should they know and care about how the works came together? What if the collection, like Dr. Leopold's, involves art whose ownership might have been clouded by Nazi plundering? And what is the museum's duty when an owner appears to be damaging works?
To some art lovers, Dr. Leopold is a genius who recognized the importance of Schiele, Gustav Klimt and other Austrian Expressionists long before the world did.
To others, who told their stories over the past two months, Dr. Leopold is too passionate a collector, someone who badgered and manipulated owners until they sold him their treasures, often at a very low price. In the Bondi case, he simply discounted her claim. He says he bought the painting legitimately.
Equally troubling to art experts already upset by his restorations, Dr. Leopold, as the self-declared ultimate authority on Schiele, has alienated some scholars and museums by denying them access to his holdings and, when he does lend, by frequently demanding control over curatorial details.
''This is his life,'' said Magdalena Dabrowski, the senior curator at the Modern who organized the exhibition. And he concurred, adding in slow, accented English, ''my whole life.'' Dr. Leopold has told several people that he is Schiele reincarnated.
In a telephone interview from Vienna, Dr. Leopold indicated nothing but pride in his collecting activities, disputing some stories as lies. And he took pleasure in his role of bringing attention to Schiele.
At the Modern, Glenn D. Lowry, the director, defended the museum's position. ''We are showing this collection because we think Schiele is an extremely important artist, and Leopold has the finest group of Schieles anywhere,'' he said. ''As it comes under public scrutiny, a great deal of information will come out about it: some problematic, some not. But one must be very careful about applying the standards of today to things that happened in the past.''
And so, on Oct. 9, the eve of the Schiele exhibition's opening, the Modern feted Dr. Leopold with a black-tie dinner. Ronald S. Lauder, the museum's chairman and himself a collector of Viennese art, began his speech by declaring his jealousy of Dr. Leopold. Mr. Lauder, who is also chairman of the World Jewish Congress's new commission to recover art taken from Jews during World War II, helped finance the exhibition. He declined to comment on Dr. Leopold or the show.
Although it is clear that the Modern did not know the whole of Dr. Leopold's story, he is well known in some sectors of the art world, and some of his activities have been questioned before. He was, for example, once sued successfully by Schiele's sister Melanie Schuster, who said Dr. Leopold had enticed her to trade some watercolors and drawings that she inherited for some of the artist's early oil paintings, which were less valuable.
She also said Dr. Leopold had tricked her into signing a receipt that she thought was a loan document, according to a 1990 article on Dr. Leopold in Art and Auction magazine. The 1974 settlement required Dr. Leopold to return more than 60 works and give her more money, while she was ordered to give him three paintings, the magazine said.
Ms. Dabrowski, who said she knew of the lawsuit and had heard some rumors about Dr. Leopold's acquisition tactics, said that such issues never came up in discussions at the Modern or in her research for the show's catalogue. ''I didn't want to go into it,'' she said. ''My essay was about Schiele, not Leopold.''
That explanation resonates with other museums. ''How a collection is assembled doesn't come up when a museum takes a collection for exhibition,'' said Thomas R. Krens, the director of the Solomon R. Guggenheim Museum, which showed some of Dr. Leopold's holdings in 1965. ''If a collection you had never heard of shows up on your doorstep, that's different. It would demand scrutiny. But this collection has been shown at the Royal Academy and at other institutions, and it has been written about in a serious way, so that gives the impression that most of these questions have been vetted.''
''There are a lot of tough people who collect art,'' he added. ''It's not a general thing for a museum to do F.B.I. reports.''
The Pursuit : A Passion Begun In Student Days
The annals of art collecting are indeed flush with eccentrics. But even among them, Dr. Leopold stands out.
Tall, slender and attentive to his appearance, Dr. Leopold lives with his wife in a traditional Austrian house in Grinzing, the quaint wine-village area of Vienna. It is the house he grew up in, and it was, until he reached his pact with Austria, jammed with art of the late 19th and early 20th centuries, including 10 major works by Klimt, 2 master works by Oskar Kokoschka and the most comprehensive group of Schiele's works in the world.
''There is drawer after drawer of drawings, almost organized by the month'' they were made, said Mr. Krens of the Guggenheim, describing his visit a few years ago. And there is -- or was, now that most is in storage for the museum -- Wiener Werkstatte furniture; Oceanic, African and Egyptian art, and even medieval armor.
Dr. Leopold began buying art as a medical student in 1950, when the market for Schiele and Klimt was slight. Not wealthy, he borrowed from banks, bought a lot and actively traded mediocre works for better ones, bargaining hard and parlaying his greater knowledge into an advantage over the seller. ''If you don't pay the best price because you are not a Rockefeller, you have other ways to get your collection,'' explained Klaus A. Schroder, the director of the Kunstforum in Vienna and since mid-1996 managing director of the soon-to-be-built Leopold Museum.
Persistence was one weapon. Dr. Leopold would repeatedly call the owners of works he coveted, even in the middle of the night. Sometimes, he wore down resistance in person. Once, for example, he wanted a Klimt whose owner declined his offers. ''She said, 'I won't sell, go away, you're not welcome here,' '' said Wolfgang Fischer, a Viennese dealer who has known Dr. Leopold for decades. ''But when she came back from the theater late at night, he was there sitting on a stool on her doorstep. He doesn't accept no for an answer.''
Another time, Mr. Fischer and Dr. Leopold were competing for a collection owned by an Austrian woman who had fled to Australia. ''One day, I called Australia to ask if my offer was acceptable,'' Mr. Fischer said. ''I thought I got her son, who said his mother was not available. Later I found out that Leopold bought the collection.'' He had flown to Australia to woo the owner.
The story did not end there. ''Later,'' Mr. Fischer recalled, ''he said to me, 'Didn't you ring up the lady?' And when I said yes, but I had spoken only with her son, he said: 'You're wrong. It was me you spoke to.' He was sitting in her house.''
The Treasures: Relentless Pursuit Of His Quarry
Years earlier Dr. Leopold had tracked two major Schiele paintings, ''Hermits'' and ''Poet,'' both on view at the Modern, to Arthur Stemmer, a Jew who had fled Austria for London. ''Leopold was quite persistent, and my stepgrandfather was very disappointed by the prices he offered,'' said Thomas Neurath, the chief executive of Thames & Hudson, the London art book publishers.
Recalling that ''it was a tormented topic'' around his house, Mr. Neurath said: ''Stemmer felt the price was low, even acknowledging the fact that Schiele was hardly known outside Austria in those days. But he had no choice, because the money was needed.''
Dr. Leopold disagreed. ''Mr. Stemmer was very glad to get this price,'' he said on the phone, recalling the amount he paid for ''Hermits'' at $10,000 to $15,000 in today's dollars. ''For me, that price was more difficult to pay than the last Schiele painting I bought,'' which he said was a watercolor purchased for $1 million two years ago.
Today ''Hermits'' is probably the most famous painting in the collection, worth millions.
On at least two occasions, Dr. Leopold obtained paintings that had been lost by Viennese Jews, by dealing not with them but with the Belvedere, a palace that houses Austria's collection of modern art. Heinrich Rieger, a well-known collector with two Schieles, ''Cardinal and Nun'' and ''The Lovers,'' died in the Theresienstadt camp near Prague. After the war, Austrian courts awarded them to his son, Robert.
But Robert Rieger had emigrated to the United States, and the Austrian Government wanted the paintings for the nation. ''My cousin agreed and sold them to the Belvedere,'' said Phillipp Rieger, who lives in Vienna. ''He had a wife and a child. He needed the money.'' Robert Rieger knew Dr. Kallir, the Manhattan dealer, and could have sold the works in New York, his cousin said, but he sold them in Austria, ''because it was a sentimental thing.''
Robert Rieger had stipulated that the paintings remain in the national collections and labeled as a memorial to his father, his cousin said. He said both he and Robert, who died about six years ago, were surprised when ''Cardinal and Nun'' turned up in the Leopold Collection. ''He was so upset and depressed every time he saw the listing in any catalogue,'' Phillipp Rieger said. ''I asked him to write and ask, but he said it upset him so much.''
Mr. Rieger, who is 81, recently decided to inquire. In September, he wrote to the Belvedere and was told that ''Cardinal and Nun,'' which is also on view at the Modern, was given to Dr. Leopold in exchange for a Klimt painting, a Dutch landscape and a gothic sculpture.
The museum said that its files did not show that it bought the paintings ''only under the condition'' that they would always be designated as having once been part of Heinrich Rieger's collection.
Mrs. Bondi fared worse. The melancholic ''Wally'' was confiscated from Welz -- who was detained by American officials as a war crimes suspect until at least the spring of 1947, according to the United States National Archives -- and put in the Belvedere. There, it appears to have been mixed in with works belonging to Mr. Rieger; museum records say it was purchased from Robert Rieger in 1951. Whether or not officials at the time knew of Mrs. Bondi's pleas for restitution is unclear. But Dr. Leopold ignored them.
''She said it was hers,'' he said. ''And she asked me to speak to the Austrian gallery. They said they thought they got it honestly, and Mrs. Bondi did not speak with them.''
In the current exhibition catalogue, Dr. Leopold lays out the path he says ''Wally'' took. After listing Lea Bondi Jaray, in ''Vienna, later London,'' as owner, it cites Heinrich Rieger, in Vienna; Heinrich Rieger Jr., in London, and the Austrian National Gallery.
But there never was a Heinrich Rieger Jr., Phillipp Rieger said, and Robert never lived in London. Nor does the listing square with the Belvedere's records.
Otto Kallir's 1966 Schiele catalogue raisonne cites no Rieger ownership of ''Wally,'' and the Galerie St. Etienne, which today is owned by Kallir's descendants, has a letter written by Robert Rieger stating that his father never owned the picture.
Oddly, Dr. Leopold's own catalogue raisonne of Schiele's works, which he published in 1972 ''to correct Kallir,'' accepted Kallir's provenance for ''Wally.''
Despite Mrs. Bondi's many letters to Austrian lawyers, she never sued for restitution, partly because she lacked the financial resources, her family and friends said. She never sent the advance her lawyer had requested to pursue her claim. As the years passed, no other family member tried to get back the painting. ''It became futile, and the family spent its time trying to survive,'' said Gideon Southwell, a relative who lives in London.
''Leopold knows the picture belongs to my great-great-aunt,'' he said. The family considered staking a claim several years ago, Mr. Southwell said, but ''we don't have anything substantive enough to repossess the painting.'' The situation still hurts, however. Edith Southwell, Gideon's mother, said that ''when it was displayed at the Royal Academy, my Aunt Gertrude said she felt like chaining herself to the picture to get acknowledgment.''
The Legacy: A Constant Battle To Keep Control
Through the years, Dr. Leopold has fought to control Schiele's artistic legacy. He feuded with Kallir, who had known Schiele (a victim of the 1918 flu epidemic) and who compiled the first catalogue raisonne of his works in 1930. Mr. Fischer, the Viennese dealer, said of Dr. Leopold: ''He was very jealous about anyone writing about Schiele. In the 1960's, his wife took me aside and said, 'How much would it be if you don't write about Schiele?' I said there is no price to keep me from writing about Schiele.''
When Dr. Leopold lends the works, he likes to hang them himself, casting the exhibition's curator aside. The Modern, in fact, insisted on spelling out in the contract with him that Ms. Dabrowski would hang the works in New York. ''We were obliged to send him a floor plan,'' she said. ''But the decision in the installation was in the hands of the curator.''
Because of the short lead time on the Modern's exhibition, however -- the Leopold Collection show filled a gap created when Mr. Lowry, the museum's director, canceled an expensive exhibition of postwar European art -- Ms. Dabrowski was forced to accept the bulk of Dr. Leopold's catalogue. His descriptions, which ignored the lewdness of Schiele's works in favor of comments on their line and color, were criticized by the Columbia University historian Simon Schama, writing in The New Yorker. Mr. Schama misattributed the descriptions to Ms. Dabrowski, who then wrote the magazine distancing herself from them.
Much more disturbing to art experts than his interpretations are his restorations. Despite his lack of training, he has retouched several works. Dr. Leopold has also had some paintings relined with an outdated method that can destroy their texture and cause discoloration, art experts said. ''Everybody knows that he is not a restorer,'' said Mr. Schroder, the museum official. ''But he has a lot of experience in his life. It could be that nowadays restorers would handle things differently than he did. The methods have changed, but he is an old-fashioned man. He keeps doing it the old way.''
For his part, Dr. Leopold said that ''the criticism is only from my enemies.'' He said he has had paintings relined to ''keep them for our sons and the sons of our sons.''
''Only the dealers don't like it,'' he continued, ''because collectors without knowledge think a relined painting has many damages.'' He said there were no discolorations in, for example, ''Hermits,'' which has been relined twice. Both Ms. Dabrowski and Mr. Lowry, however, said ''Hermits'' was discolored. But Mr. Lowry said museums typically do not involve themselves in such matters. ''It's not our call to determine restoration,'' he said.
The Deal: A License to Give And to Receive
In Austria, the attention surrounding Dr. Leopold also hinges on costs and special treatment. When the Austrian press reported that he had for years neglected to pay the national wealth tax, the Government passed what has come to be called the Leopold Law absolving him and other collectors of the levy, if they give the public access to their holdings.
When he wanted both to reap rewards for his collection and to say he had partially given the works to the nation, officials told appraisers to ignore two rules of their trade: They were to value each work separately, instead of applying the so-called blockage discount used when many works are put into the market simultaneously, and they were told to value each work in the international market, even though virtually nothing in the collection can be exported from Austria.
The final deal, which was concluded after much debate and before Dr. Leopold provided a complete inventory, valued his holdings at about $560 million (at current exchange rates), which experts say overestimates the value by perhaps three times. Dr. Leopold is to receive about $175 million, beginning with a payment of about $63 million, some of which went to repay bank loans. Additional installments stretch to the year 2007. As director for life of the museum, Dr. Leopold also gets a monthly salary, which Austrian publications said exceeds $6,000, a figure that Mr. Schroder declined to confirm.
''Clearly this was delicate,'' said Mr. Krens, the Guggenheim director, who has longstanding ties with the Austrian Government. ''He assembled a national collection, and he put it in terms of it would be sold or dispersed, so it was entirely logical for the Austrian Government to acquire it.''
Dr. Leopold's negotiations at home had repercussions for the Modern, which had to obtain insurance for the inflated value of the works on display, a bigger sum than it had anticipated. For the museum, ''it was a fairly expensive exhibition, but it was not among the most expensive,'' Ms. Dabrowski said. Mr. Lowry, who declined to provide any cost figures, acknowledged that ''the insurance value was high,'' but said it was not that much higher than the museum's estimate.
Early this month, the Leopold Museum was granted the last of the necessary city and state approvals and permits. Construction of the nearly 130,000-square-foot building -- almost two-fifths the size of the Modern -- is slated to begin in April, with the grand opening in 2001 or 2002.
''I'm glad Vienna has a chance to show the collection,'' said Mr. Schroder, who had heard some tales of Dr. Leopold's escapades but had no comment on them. He has his hands full: the Austrian Government installed him as managing director to bring order to the museum, against the wishes of Dr. Leopold.
As for Dr. Leopold, he is still active in the art market. Now, flush with new funds, he is said by dealers and other collectors to be paying high prices at auctions, largely for 19th-century works.