LONDON’S Royal Academy of Arts is drawing excited crowds with its exhibition “From Russia: French and Russian Master Paintings 1870-1925 From Moscow and St. Petersburg.” These 120 Impressionist and Modernist masterpieces couldn’t be shown, however, until Britain acceded to a very unusual condition: that Parliament enact special legislation providing complete immunity to Russia from anyone claiming ownership of these paintings, some of which were seized by the Communists during the Bolshevik Revolution.

Art lovers may be delighted to see artworks long held in secret by Russia, but the sad truth is that the British government and the Royal Academy are now complicit in the theft of private property. If other countries follow Britain’s lead and pass “immunity from seizure” legislation in the hopes of playing host to “From Russia” or similar shows, the results will be far more pernicious than anyone can imagine.

There is, after all, far more at stake than the paintings temporarily hanging in the Royal Academy. Still hidden within Russia are many of the great art treasures that disappeared from Soviet-occupied territory in Europe at the conclusion of World War II. That’s why Russian authorities demanded such extraordinary measures to protect these paintings in Britain. Even the possibility of a restitution case could open up that Pandora’s box, a trove of long-lost art valued by some experts at $15 billion, perhaps more.

Long before the war, Hitler planned underground storage facilities large enough to hold all the artwork the Nazis could systematically plunder from the great European museums and private collections across the continent.

What Hitler began, Stalin finished. From 1945 to 1948, vast trainloads of looted “trophy art” was delivered from areas “liberated” by Soviet troops. It was of no concern to Stalin that Russia had signed the 1907 Hague convention on Land Warfare, which prohibits the plunder of cultural property (it remains in force today). Nor did he care that the Soviets made repeated assurances during Allied conferences that they would respect such property.

Admittedly, some art treasures made their way back to the Britain, France and the United States. In 1945, the Army discovered, hidden in a salt mine in Central Germany, hundreds of paintings that once hung in the Kaiser Friedrich Museum in Berlin. When the art was shipped to America — the only known officially sanctioned transfer from the American zone of occupation — the result was a groundswell of criticism. The paintings were returned to Germany a few years later.

Of course, there were G.I.’s who brought home trophies of their own, including some very valuable items like the manuscripts from a church in Quedlinburg, Germany. But this was in contravention of United States policy, not in furtherance of it.

By contrast, the Soviet Union never returned the overwhelming majority of its twice-stolen Nazi treasures and for decades refused to acknowledge it even had them. In the 1950s, the Soviets did return over a million cultural pieces to East Germany — but millions more remain hidden away. Today, the few artworks Russia trickles out are, like the Royal Academy exhibition, offered only under the strictest conditions protecting the government from any claims by lawful owners.

Other European nations have enacted laws committing themselves to determine rightful ownership and act accordingly. But in 1998, Russia legalized its seizure of “war trophies,” justifying whatever artworks in its possession as “restitution in kind,” necessary to offset the plunder of the Soviet Union by the Nazis. But on this point international law is clear: where restitution is appropriate it must be done by means of bilateral or multilateral agreements, not unilateral actions.

The 1998 Russian law does make an exception for the property of Holocaust victims, or of others persecuted by Nazis because of race, religion or ethnic identity. There have, however, been practically no claims by Holocaust survivors or their families for the simple reason that Russia has not come forth with an honest accounting of what exactly it has. (Russian authorities did recently set up a Web site listing artworks and items looted by the Nazis from the Soviet Union during the war. Which is a far cry from a comprehensive inventory.)

Some people may believe that British acquiescence to Russian demands is the only way to bring stolen art out into the open, but governments that make shameless deals and museums that profit from these exhibitions only excuse Russia’s thefts. And moral and legal options are available: one need only think of the French-Israeli exhibition now hanging in Jerusalem, whose purpose is stated clearly in its title, “Looking for Owners: Custody, Research and Restitution of Art Stolen in France During World War II.”

Everyone, including Russia, stands to gain from a full and public disclosure of the privately owned cultural properties in Russia’s hidden repositories. Only then can a real accommodation be reached whereby Russia is credited for allowing the world and its own citizens to view these art treasures, and the rightful owners gain some measure of restitution or compensation.

Allan Gerson is a former professor of international law and senior State and Justice Department official.

Copyright 2008 The New York Times Company