MOSCOW, APRIL 13 -- The Soviet Union admitted today with "profound regret" that Joseph Stalin's secret police murdered nearly 15,000 Polish officers at Katyn Forest in 1940.

After decades of insisting that Nazi soldiers had executed the captured Polish officers a year later, the Kremlin issued a statement saying the government "declares that this tragedy is one of the gravest crimes of Stalinism."

Like its recent apology for the invasion of Czechoslovakia in 1968, Moscow's admission of guilt today is a dramatic and long-awaited step in Kremlin leader Mikhail Gorbachev's declared intention to fill in the "blank spots" of Soviet history and to heal the longstanding resentments of the countries of Eastern Europe.

Polish President Wojciech Jaruzelski, who met today with Gorbachev, is scheduled to visit Katyn, near the city of Smolensk in western Russia, on Saturday.

"The graves of the Polish officers are next to the graves of Soviet people who were brought there by the same evil hand," Gorbachev said during a luncheon with Jaruzelski. "To speak about this is not easy, but it is necessary, because it is only through truth that we find the road to genuine renewal and genuine mutual understanding."

Gorbachev gave Jaruzelski copies of two cartons of documents found in the archives of the Soviet secret police which list the names of the dead officers and prove Stalin culpable in the massacre.

The murders of the officers, who were captured by the Red Army when it invaded eastern Poland in September 1939, have haunted Polish-Soviet relations for a half century. For many Poles, the Katyn massacre was the most brutal embodiment of the Soviet Union's imperial ambitions in their country and Stalin's attempt to wipe out the Polish military and intellectual elite.

Gorbachev said the Katyn issue had been a "historical knot" in Soviet-Polish relations and said that "for us it is no secret" that many Poles still resent the Soviet Union.

Speaking in Gdansk, Solidarity leader Lech Walesa said: "It is good that the murderers admit their murder. But they must remember that this is only part of the problem. This crime was even more heinous than the Hitler crimes." Walesa said that there still remain questions of punishment of the guilty and compensation to the families of the victims.

When Polish Prime Minister Tadeusz Mazowiecki visited Katyn in November he demanded that Moscow provide "moral" compensation not only for the deaths of the officers, but for the thousands more Poles who died in Soviet labor camps over the decades.

Gorbachev clearly preferred to make the apology while Jaruzelski, a Communist ally, was in Moscow rather than to a Solidarity leader such as Walesa or Mazowiecki. Especially for Soviet conservatives, who have bemoaned the "loss" of Eastern Europe in 1989, the admission of guilt at Katyn undermined the legitimacy of the Soviet Union's dominance of Poland in the postwar era.

The government statement said that Soviet archivists and historians "just recently" discovered documents in the files of the secret police showing that 394 of the 15,000 Polish officers kept in three prison camps were turned over to one camp, while the rest were turned over to the NKVD (the forerunner of the KGB) near Katyn in the Smolensk region.

"The discovered archival material puts direct responsibility for the atrocities in the Katyn Forest" on Stalin's notorious secret police chief, Lavrenti Beria, his deputy Vsevolod Merkulov and other "henchmen," the statement said. Beria and Merkulov were executed in Moscow after Stalin's death in March 1953.

The attempt to make this latest admission appear like the end of a long scholarly quest rather than a political decision is reminiscent of the government's recent archival "discovery," after decades of denials, that the Soviet Union had in fact signed a series of secret protocols with Nazi Germany in 1939 that led to Moscow's occupation of eastern Poland that autumn and its annexation of the Baltic states the following year.

In a recent interview, historian Yuri Afanasyev recalled how, as a student at Moscow State University in the 1950s, "friends from Poland told me exactly what happened at Katyn. It was a revelation then, perhaps, but you had to have had your eyes closed if you believed the official versions in the past 30 years."

Moscow long maintained that the invading Germans had killed the Polish officers at Katyn in 1941. But historians outside the Soviet Union, and even some independent scholars here, say that the murders took place in the spring of 1940, a year before the Nazis occupied the Smolensk region. When a Polish military leader asked Stalin in 1941 what became of the thousands of officers, Stalin said: "They fled. To Manchuria."

According to historians Mikhail Heller and Alexander Nekrich, "the Katyn massacre was entirely in keeping with Stalin's main political aims: to purge Poland of all patriotic elements, to wipe out the intelligentsia and thus to clear the ground for a pro-Soviet regime."

A similar view was taken in a groundbreaking article published last month in the liberal weekly Moscow News. Historian Natalya Lebedeva, who found army documents showing that the officers were transported to mass execution sites, said that 15,131 people "disappeared into nowhere."

German troops found more than 4,000 bodies in mass graves in Katyn in 1943. Polish Red Cross specialists determined then, by examining documents found in the uniforms of the dead officers, that the shootings had taken place in 1940. Last year, a Polish newspaper caused a sensation when it published a copy of the Red Cross report that had been found in the archives of the British Foreign Service.

The Katyn forest, a beautiful wood of birch and pine, was a zone forbidden to foreigners until two years ago when the two sides set up a joint commission to investigate the dispute. Poland's leading filmmaker, Andrzej Wajda, was recently in Moscow and told reporters that he was making a film about the massacre. His father was shot and buried, but never found, in Katyn.

Until last year the grave marker in Katyn said the massacres were the work of "Hitler's fascism." Now it reads just "Katyn 1940."