Russian President Boris Yeltsin has acknowledged that an epidemic of anthrax in the Ural Mountains about 12 years ago was caused by military researchers trying to make a germ weapon, not by natural causes as previously claimed by senior officials of the former Soviet Union.

Yeltsin's unusual public statement -- an admission that the Soviet government hid the truth for a long time on an issue of importance to Washington -- is being taken by U.S. intelligence analysts as a final vindication of the view they first put forward in 1980. Their claim was criticized at the time by some U.S. allies and independent U.S. experts who said it was based on thin evidence.

The mysterious outbreak of anthrax in 1979 in the city of Sverdlovsk 850 miles east of Moscow, which caused scores of deaths, initially attracted only brief notice in the Soviet emigre press. But in early 1980, it was catapulted suddenly onto front pages around the world when the Carter administration said the cause was "inadvertent exposure . . . to some sort of lethal biological agent."

The Reagan administration subsequently made the event the principal basis for its annual claim that Moscow was violating an international treaty barring work on germ weapons. But U.S. skeptics said they wondered if Washington was skewing the evidence as the Cold War heated up.

Yeltsin made his statement about the notorious incident in a May 27 interview with a Russian mass circulation daily, Komsomolskaya Pravda, that attracted little public notice. It was brought to the attention of a reporter here by a senior Russian official who, on the eve of Yeltsin's summit meeting with President Bush, characterized it as an example of the Russian president's commitment to expose the truth about ugly activities that Soviet leaders before him tried to conceal.

Last week, Yeltsin also disclosed in a letter to Congress that a dozen Americans shot down over Soviet territory in the 1950s had been secretly kept in Soviet prisons and psychiatric clinics. He said in the Komsomolskaya Pravda interview that he already has revealed the secret tale of Sverdlovsk to Bush, British Prime Minister John Major, and French President Francois Mitterrand, and that he has also signed a decree barring any future germ weapon activities by the Russian military.

Yeltsin, who in 1979 was the head of the Communist Party in Sverdlovsk, may have felt a personal compulsion to set the record straight in a public statement at home. The Russian press in the past year has printed a dozen or so articles alleging a government coverup of military involvement in the tragedy that also raise questions about what Yeltsin knew.

Yeltsin explained in the brief portion of the interview touching on Sverdlovsk that he said nothing previously because "nobody has asked me about it." He then disclosed that, even as Moscow officials were telling the world the incident was not associated with military activity, the KGB had admitted privately to him that "our military development was the cause."

Yeltsin said he responded by going to KGB chief Yuri Andropov, who in turn called Defense Minister Dmitri Ustinov "and ordered {him} to liquidate these facilities completely." But Yeltsin said he learned later that the military's laboratories in Sverdlovsk "had simply been moved to another region and the development of this weapon continued."

Western suspicions about the incident were partly aroused by the fact that anthrax is highly lethal and persistent in soil, making it a top candidate for biological warfare. A British island used for testing anthrax-filled bombs produced in collaboration with the United States during World War II remains dangerously contaminated today.

But the Soviet explanation that the anthrax outbreak came from natural causes also had at least the ring of truth. Officials maintained that spores indigenous to the region's soil were spread among cattle through ingestion of contaminated bone meal and among humans through the illegal sale of diseased cattle from private farms. Limited outbreaks of anthrax among U.S. farm animals have been caused by contaminated feed.

A skeptical 1986 Defense Intelligence Agency report listed "hundreds of deaths" in the first week of the outbreak and attributed the severity and type of illness to inhalation of spores released accidentally by a military research center. But senior Soviet health officials stubbornly insisted in a 1988 presentation at the National Academy of Sciences in Washington that the deaths were many fewer, much slower and due solely to eating tainted meat.

U.S. specialists such as Philip Brachman of Emory University, Matthew Meselson of Harvard and Alexander Langmuir, former chief epidemiologist at the Centers for Disease Control, said following that presentation they considered the Soviet claim plausible although not completely proven.

One of the first major cracks in the official tale inside Russia came last November in Komsomolskaya Pravda, which reported that people living near a military research center in Sverdlovsk remembered seeing "a discharge in the form of a pink cloud that rose behind the high fence." The article also quoted a deputy chief for science at the research center acknowledging that the facility was conducting experiments in 1979, allegedly to develop an anthrax vaccine.

Izvestia, a popular newspaper formerly controlled by the government, subsequently printed damning allegations from a retired general, A. Mironyuk, who was a senior official in the Ural Military District at the time. Mironyuk said he learned from the KGB that "someone from the laboratory arrived early in the morning and began to work without turning on safety filters and other protective mechanisms."

The resulting discharge swiftly claimed both military and civilian victims downwind, Mironyuk said. "Only after they were pinned to the wall did the specialists confess. It was then that an entire program to disinform the public in the country and the world was developed," the retired general said.

The newspaper explained that a second anthrax outbreak several weeks after the accident was provoked when workers failed to don respirators during a massive cleanup operation, not by delayed sales of tainted meat as officials had claimed. The cleanup of the laboratory itself lasted five years and required the replacement of floors and ceilings.

Mironyuk said some of the laboratory equipment was secretly transported to Irkutsk. "Naturally I carried out" an order to burn all related documents, he said. Izvestia reported that the chief of the military base committed suicide.