The National Gallery of Art announced yesterday that it will relinquish a valuable still life by the 17th-century Flemish artist Frans Snyders after concluding that the painting was almost certainly looted by the Nazis from a French Jewish family during World War II.

The announcement followed 18 months of research into the tangled history of the painting, whose previous owners included Luftwaffe chief Hermann Goering, the number two man in the Nazi regime, and Karl Haberstock, Adolf Hitler's favorite art dealer. The painting, "Still Life With Fruit and Game," was donated to the National Gallery in 1990 by a wealthy New York art dealer who is himself a Jewish refugee from Nazi Germany.

"It's a wonderful painting," said Arthur Wheelock, curator of northern baroque painting at the National Gallery. "We hung it with great pride." The color-drenched oil on canvas was exhibited alongside works by other Flemish artists such as Peter Paul Rubens and David Teniers II, but was taken down several weeks ago after the gallery concluded that it had been looted.

The National Gallery's wrenching decision to part with its only Snyders painting is a dramatic illustration of the way in which the issue of Nazi-confiscated artwork has come to haunt American museums over the past few years, part of a worldwide controversy about Holocaust era assets. Art experts believe that hundreds, perhaps thousands, of artworks looted by the Nazis ended up in American collections after the war.

Three other American institutions--the North Carolina Museum of Art, the Art Institute of Chicago and the Seattle Art Museum--have acknowledged that paintings in their possession were stolen by the Nazis from European Jews during the course of World War II and were never restored to their previous owners. But this is the first time that a publicly funded federal institution has agreed to part with a Nazi-looted artwork.

National Gallery officials said they were approached earlier this year by the heirs of a prominent French Jewish art collector, Edgar Stern, who identified the Snyders painting on the National Gallery Web site (www.nga.gov). The heirs were able to provide the gallery with important additional evidence linking the painting to one that had been seized from the Stern family collection in Paris in early 1941, soon after the Nazi takeover of northern France.

"Both sides are in agreement that this was a stolen work, and now the Sterns are providing the National Gallery with a list of heirs, including a genealogical tree," said Hector Feliciano, an international art sleuth working with the Stern family and author of "The Lost Museum: The Nazi Conspiracy to Steal the World's Great Works of Art."

Gallery officials said they wanted to make sure that they returned the picture to the true heirs. According to Feliciano, the painting has been claimed by a group of four heirs led by Edgar's grandson Gerard, who splits his time between France and Switzerland. The Stern family declined to be interviewed but authorized Feliciano to speak on its behalf.

The ownership history, or provenance, of the Snyders painting provides an insight into the extremely complex business of tracking down looted artworks and restoring them to their rightful owners. It was assembled painstakingly over the last two years as part of a huge effort by the National Gallery to vet the 3,175 paintings in its collection, including 1,600 that were in Europe between 1933 and 1945 and could conceivably have passed through Nazi hands.

A French government commission on Holocaust era issues recently estimated that a total of 40,000 paintings and other art objects looted by the Nazis from France during World War II remain missing.

Gallery officials said they had no idea of the Snyders work's true history when they accepted the painting in 1990 as a 50th-anniversary gift from Herman Shickman, a prominent New York art dealer who fled to the United States from Nazi Germany in 1938. The first suggestion of a possible problem with the painting surfaced in April 1999 when Wheelock, who was researching the gallery's Flemish holdings, came across the Snyders still life in a catalogue of paintings that had once belonged to Haberstock.

The Haberstock connection was an immediate red flag to Wheelock and his fellow National Gallery curators. Known for his opulent lifestyle and anti-Semitic views, Haberstock had a string of Nazi clients, including Hitler and Goering, who amassed vast amounts of art during World War II, much of it looted from Jewish collectors in France and other German-conquered countries.

"He was the most important art dealer in the Third Reich," said Jonathan Petropoulos, an art historian at Claremont-McKenna College in California and one of the world's leading experts on Nazi-looted art. Business ledgers recently unearthed by Petropoulos show that Haberstock began selling artworks to Hitler in 1936, after which he leapt into the inner sanctum of Nazi cultural bureaucrats.

Further provenance research established that Haberstock had acquired a Snyders still life--with almost identical dimensions to the National Gallery painting--from Goering in June 1941 in exchange for a work by the 19th-century Austrian painter Hans Makart. Goering, who prided himself on being an art connoisseur, had picked out the Snyders while on an inspection tour of the Jeu de Paume, the Paris art museum that became a warehouse for Nazi-looted art during the war.

Nazi records showed that the Goering Snyders had been looted from the Paris apartment of Edgar Stern's widow, Marguerite, who remained in Paris throughout the war and managed to avoid deportation despite her Jewish background. The Stern collection was just one of about 50 important art collections belonging to French Jews that were seized by the Nazis and taken to the Jeu de Paume.

As with the other confiscated collections, the Nazis meticulously labeled and catalogued the Stern artworks, using the initials ST as an identifying mark. The National Gallery Snyders bears the ST initials scrawled over the back of the canvas, a further indication that it was part of the looted collection. The Stern heirs were able to clinch their claim to the still life when they provided curators with photographs of the backs of other Nazi-confiscated Stern pictures with similar markings.

Precisely what happened to the still life after the war is somewhat unclear, although the broad outlines of the story have been established. National Gallery researchers believe Haberstock gave the painting to a close collaborator, Baron von Poellnitz, an aristocratic Nazi who owned a magnificent Bavarian castle north of Munich. Both Haberstock and von Poellnitz were detained by American troops who were investigating Nazi art looting, but were later released and permitted to resume their art-dealing activities.

According to the official National Gallery provenance, in about 1968 von Poellnitz sold the Snyders painting to Shickman, the Manhattan dealer who had fled Nazi Germany three decades earlier. This version of events is disputed by Shickman, who says he never knew von Poellnitz; he maintains that he bought the painting from the Brod art gallery in London. In a telephone interview yesterday, Shickman said he had no idea that there was a problem with the painting.

Shickman said he agreed to donate the painting to the National Gallery as part of its 50th-anniversary celebration "because I felt I owed something to this country." He described the painting as one of Snyders's finest works but declined to put a value on it. According to Christie's auction house, Snyders's paintings have recently fetched prices ranging from $40,000 to $1.5 million.

Among the intriguing questions raised by the case is whether Shickman owes back taxes now that questions have been raised about the provenance of the painting. Gallery officials persuaded the Internal Revenue Service to allow donors to deduct the full value of works of art from their taxes. The market value of a painting known to have been looted and never returned to its rightful owners is zero.

Gallery officials said their research had turned up some "contradictory evidence" about the provenance of the still life, including confusion over the title of the painting. Archival documentation of the Stern picture repeatedly refers to "hares" while the animal in the gallery painting appears to be a small deer. A gallery statement said that, despite such inconsistencies, the trustees nevertheless concluded that the painting belonged to the Stern family and "approved the return of the work" on receipt of assurances that Gerard Stern represents all the Stern heirs.