PARIS -- jan vermeer's "The Astronomer" has an unsightly scar on its backside. If you were to pull the famed painting from its hook in the Louvre's Richelieu wing, you would see the spot where a black swastika once marked it as a prized possession of the Nazi regime. So were countless works by the likes of Picasso, Renoir and Rodin, all of them stolen by the Nazis from French museums and private art collectors during World War II.

Almost as unsightly was what happened to those paintings after the war -- this time at the hands of the French government. While "The Astronomer" found its way back to its original owner (it was legitimately donated to the Louvre in 1982), thousands of other paintings and treasured art possessions were kept away from war victims and their heirs by French museum authorities.

Hector Feliciano, a Paris-based Puerto-Rican journalist, ranks France right alongside Switzerland as a covert hoarder of Nazi war loot. He comes to that conclusion in "The Lost Museum: The Nazi Conspiracy to Steal the World's Greatest Works Of Art" (Basic Books), a seven-year investigation that has left a red-faced French government scrambling to explain just how so many stolen works of art have yet to be returned to their rightful owners 52 years after the end of the war.

The art in question was looted by the Nazis during World War II. In addition to paintings hanging on French museum walls, approximately one-third of the 203 known private art collections in the country were also looted. Most of the private collectors' art was included in a 61,257-work bundle returned to the French government after the war with apologies from Germany. But the task of matching each work with its proper owner seems to have been too tedious for the French government to contemplate. Nothing was done until Feliciano began his investigation in 1989.

Working at the time as a cultural writer for the Washington Post, Feliciano stumbled across a puzzling statistic that claimed that 20 percent of the art returned to France by the Germans was still considered "missing." He was told by the Louvre that an inventory of the stolen works was "still in progress," a questionable claim considering that nearly 50 years had passed and that the obsessive-compulsive Nazis had left meticulous catalogs detailing each work's history and artistic value.

After several failed attempts at conferring with the museum's curator and legal department -- and being dismissed as an insignificant meddler -- Feliciano set about matching the stolen art with its original owners himself. It proved not to be nearly as difficult as the French authorities claimed. Art, being of such personal and financial worth, almost always leaves a detailed paper trail documenting who bought what, when and where. Through countless interviews and visits to archive rooms around the world, Feliciano turned up thousands of paintings -- Manets, Monets, Cezannes, a Pieta by Michelangelo, the Van Eyck brothers' Ghent Altarpiece -- that the French government had publicly labeled as still "stolen."

Feliciano's investigative account was first published in French as "Le Musie Disparu" in 1995. With the American version hitting U.S. bookstores this month, the French government has moved with unaccustomed swiftness to make amends. Three interlinked expositions running until mid-May at the Louvre, Orsay Museum and the Centre Georges Pompidou are serving as open invitations to those who wish to reclaim their long-lost art treasures.

While Feliciano agrees that the French government is finally coming to terms with the stolen art scandal, he remains suspicious of its motives. "If anything, these expositions are a high-profile PR job," he says. "Heirs are not going to come forward because they do not know that the art exists, or that it belongs to them." Feliciano believes that, if the government were to make a sincere effort to locate the rightful owners, the museums would start where he left off. "They have the documents," he insists. "It is not the individual's job to find the museum, it is the museum's job to find the individual."

Understandably skeptical about what will happen once the temporary expositions have finished their run, Feliciano plans to be a perpetual thorn in the museums' side. "Art is not like a shoe," he says. "For many people, regaining a lost work is the equivalent of regaining the soul of someone who perished in the war. It is often the only good aspect in an otherwise dark portion of history. It's a way to say, finally, 'Ah! The war is over.'"