WASHINGTON -- The Soviet Union under dictator Josef V. Stalin "summarily executed" some U.S. prisoners after World War II and forced others, some of whom are still alive, to renounce their U.S. citizenship, Russian President Boris N. Yeltsin said in a letter given to a Senate committee yesterday.

But Dimitri Volkogonov, the senior Russian emissary who read Mr. Yeltsin's letter to the Senate Select Committee on POW-MIA Affairs, said no evidence uncovered by Russian investigators indicates that U.S. POWs from Vietnam or the Korean War were transferred to the Soviet Union.

Mr. Yeltsin's letter spoke only in general terms of newly discovered documents indicating "the shocking facts" of some prisoners' being executed by Stalin's government "and in a number of cases being forced to renounce their U.S. citizenship."

But the letter also said that "all their rights are now fully guaranteed" and that they are free to return to the United States if they so choose. "There are no American citizens forcibly held on the territory of Russia."

U.S. authorities have suspected for years that the former Soviet Union held U.S. war prisoners, but Soviet authorities had steadfastly refused to provide confirmation.

Mr. Volkogonov, a former general, shed little light on the fates of more than 10,000 Americans still listed as missing from the Vietnam and Korean wars, but his appearance did provide the fullest public accounting of what befell Americans held captive in the Soviet Union between World War II and the end of the Cold War.

Mr. Volkogonov, co-chairman of a Russian-U.S. commission formed in March to investigate the fate of Americans missing from several conflicts, told the committee that:

* Soviet authorities detained 119 U.S. servicemen "with Russian, Ukrainian or Jewish names" from the more than 22,000 GIs they liberated from German POW camps at the end of World War II. Although most were released after U.S. protests, 18 died in Soviet custody and "some ended up staying in camps for a long time."

* The largest group of Americans imprisoned in the Soviet Union included more than 730 pilots and other airmen who either made "forced landings on Soviet territory" or were shot down on Cold War spy flights. Mr. Volkogonov was not specific on their fates but spoke generally about prisoners' being interned in labor camps, some being executed and others forced to eventually renounce their U.S. citizenship.

* Nine Vietnam-era U.S. servicemen were transferred to the Soviet Union, but they were all deserters brought to Moscow for propaganda purposes and later resettled in third countries. Although the possibility of Vietnam-era POWs' being transferred to the Soviet Union "cannot be entirely discounted," investigators have failed to turn up any documentary evidence, Mr. Volkogonov said.

* Soviet records show that North Korea held about 3,000 U.S. airmen at five prison camps along the North Korean-Chinese border during the Korean War. Although the records do not indicate that any were sent to the Soviet Union, some may have gone to China.

Calling Mr. Volkogonov's testimony a "revelation," Sen. John Kerry, D-Mass., chairman of the POW committee, said the Americans found by the commission will be contacted by U.S. officials "and asked whether they want to come home."