At least 42 people were killed in a Russian city in 1979 by a cloud of deadly anthrax spores that probably resulted from a germ warfare ac-ci-dent, according to a new study of secret autopsies.

The study, published Monday in the Proceedings of the National Academy of Sciences, said American experts determined that the victims died after breathing disease particles. The U.S. experts studied tissues and records hidden by Russian scientists after an anthrax outbreak.Dr. David H. Walker, a professor of pathology at the University of Texas Medical Branch at Galveston who examined the tissues, said the findings are consistent with some sort of germ warfare accident that sent a lethal cloud floating into a city of 1 million people.

American authorities have said since 1980 that an anthrax outbreak in the city of Sverdlovsk, 840 miles east of Moscow, was caused by a military accident, but officials of the former Soviet Union said the outbreak came from infected cattle.

Russian President Boris Yeltsin admitted in May, however, that the 1979 epidemic was caused by a military accident. He said as many as 60 died, but he gave few details.

Anthrax, usually a disease of cattle, has been used by the United States, the Soviet Union and other nations in germ warfare experiments. Such weapons are outlawed by a treaty signed by more than 40 nations, but Russian officials admitted that work on germ weapons continued until 1991.

Studies by Walker and some other American scientists and by two Russian scientists have proved that the victims of the 1979 anthrax outbreak died by breathing airborne spores of the disease.

Walker said the fact that so many people contracted anthrax pneumonia in such a short period of time in one location is powerful proof that there was some sort of germ warfare event in Sverdlovsk. Before this study, he said, there were only 11 cases in worldwide medical records of airborne anthrax.

But just what happened in Sverdlovsk is still not clear, he said.

"It doesn't tell us what generated the aerosol of spores," Walker said. "Was it an experiment leak, or a weapon that went off by accident, or an experiment that exploded? There are still questions that are unanswered."

Walker and a group of Americans visited a hospital in Sverdlovsk last year and a Russian pathologist showed them tissues, specimen slides and handwritten records of autopsies performed on 42 patients who died of anthrax in 1979.

Walker said the tissues give clear evidence that the victims breathed in airborne anthrax spores that invaded their lymph system.