MOSCOW (AP) _ The head of a Russian depository of top-secret documents has been fired because of the leak of a disputed report on the fate of U.S. prisoners of war in Vietnam, a state archive spokeswoman said today.

The spokeswoman also said the document was believed authentic, but refused to speculate about the reliability of its contents.

The document, a report to the Communist Party Politburo in North Vietnam, says 624 American aviators were prisoners in September 1972, more than listed in American or Vietnamese records.

It was discovered in the Contemporary Documentation Center in Moscow, which contains material from the archives of the Soviet Communist Party.

Stephen J. Morris, a fellow at Harvard University's Russian Research Center, obtained a copy several months ago, said archive spokeswoman Natalya Krivova.

The joint U.S.-Russian commission on American POWs got a copy only recently, Col. Anatoly Volkov, a commission spokesman, said today.

The commission, which searches for information on missing American servicemen, is co-chaired by Gen. Dmitry Volkogonov, a Russian military historian, and Malcolm Toon, former U.S. ambassador to Moscow.

On Monday, the board of the State Archives Service dismissed Rem Usikov as director of the documentation center for ''violating regulations on access to confidential material,'' said Krivova.

Usikov's deputy, Anatoly Prokopenko, was appointed head of the documentation center, she said.

She said Russian researchers found the document, supposedly written by a top Vietnamese army officer, in the archives several months ago.

Volkov said the archive did not notify the commission about the existence of the secret report. He refused to say how the commission eventually found out about the document.

Krivova said archive officials believe the document is genuine but she refused to speculate whether the information was correct.

An American presidential envoy just back from Vietnam said the document contained many flaws. He said officials in Hanoi told him it was based on ''bad intelligence.''

''We know that some of the facts that are alleged in the Russian document are wrong, a lot of the facts,'' retired Gen. John Vessey Jr. told reporters in Washington after reporting to President Bill Clinton Wednesday on his trip.

Vessey said U.S. records show that 108 American aviators were lost in Vietnam between February and September 1972. He said Vietnamese officials showed him a ledger listing 381 American aviators captured in North Vietnam through February 1972.

If the Vietnamese accounting is correct, the highest number that could have been held as of Sept. 15, 1972 would be 467 - not the 624 mentioned in the Russian document.

Morris, the researcher, said Vessey's comments misrepresented what the document said on the segregation of prisoners, the sequence of their release and other matters.

The issue of missing Americans has hampered political and economic ties between Washington and Hanoi since the end of the Vietnam War nearly 20 years ago.

It has also been a thorny issue in U.S.-Russian relations. American members of the joint commission have repeatedly accused the Russian government of withholding information that may shed light on the fate of Americans missing in World War II, Vietnam and Korea.