An unusual anthrax epidemic that killed 68 people in the former Soviet Union began when the deadly spores escaped from a covert military microbiology facility, Russian and American researchers have concluded.


Their work, based on two years of interviews with survivors of the 1979 outbreak in Sverdlovsk and unique access to Russian public health records, raises the possibility that one of the most controversial chapters in Cold War history arose from experiments that violated an international accord forbidding biological weapons.


The Sverdlovsk epidemic is the largest documented anthrax outbreak of its kind. Thousands may have been infected by rare air-borne anthrax disease spores, which can cause high fever, convulsions, lung lesions and, in severe cases, rapid death.


In an international debate over the incident, U.S. officials at the time charged that the outbreak resulted from an accident at a military plant that was mass-producing the anthrax bacterium. Soviet and Russian officials argued for 10 years that the townspeople had been infected by eating diseased meat or by natural causes. In research made public Friday in the journal Science, Russian and U.S. scientists confirmed that the infection was spread by the wind, pinpointed the day the anthrax spores escaped and traced the outbreak back to its source: a military microbiology facility known simply as Compound 19, which U.S. scientists suspect is still in operation.


"This is definitive proof," said Harvard University biologist Matthew Meselson, who led the research team.


A U.S. diplomatic official in Washington, who asked not to be identified, noted that the formal treaty violation is still an open issue. He said he hoped the new evidence concerning the origin of the epidemic would "encourage further openness by the Russian government."


Several countries, including Britain, have experimented with anthrax as a weapon in the past, but all stocks of military microbes were destroyed under the provisions of a 100-nation arms control treaty in 1972, experts said.


The United States, the Soviet Union and others that signed the treaty, however, reserved the right to produce such lethal microbes and viruses to conduct research into defensive measures such as vaccines and protective clothing.


Indeed, U.S. Defense Department spending on research into such epidemic weapons as anthrax increased six-fold during the '80s to $90 million a year.