American intelligence officials who know what Dr. Alibek said in secret debriefings after his defection in 1992 give his new account considerable credence. They have called him highly believable about the subjects he knows firsthand, like the Soviet biological weapons program from 1975 to 1992, when he served as one of Moscow's top germ warriors. He is less reliable, they say, on political and military issues that he knows secondhand.

The book asserts that Mr. Gorbachev, in his ''characteristic scrawl,'' signed a five-year plan for 1985 to 1990 that ordered the most ambitious effort ever for the development of deadly germs and viruses, including smallpox, as weapons. In 1980, world health authorities declared the ancient scourge eradicated from all human populations.

''Gorbachev's Five-Year Plan -- and his generous funding, which would amount to over $1 billion by the end of the decade -- allowed us to catch up'' with the American biological weapons program, which was making great strides, Dr. Alibek writes.

In 1988, as President Gorbachev's glasnost and perestroika reform campaigns were in full swing and the Russians and Americans were negotiating new arms control treaties, officials ''at the highest levels,'' Dr. Alibek said, ordered the arming of giant SS-18 intercontinental ballistic missiles aimed at New York, Los Angeles, Seattle and Chicago with anthrax and other deadly germs.

The secret move came as Soviet leaders publicly waged a peace offensive. In his book, ''Perestroika: New Thinking for Our Country and the World'' (Harper & Row, 1987), Mr. Gorbachev argued that for decades Western experts had falsely accused Moscow of weapon horrors and that the real engine of the arms race was the United States.

Reached through his office in Moscow, Mr. Gorbachev sidestepped Dr. Alibek's charges and questions about the germ program. His spokesman said that Mr. Gorbachev did not know Dr. Alibek, and that there was ''no sense in getting involved in an endless process of commenting.''

William C. Patrick 3d, a key figure in America's former germ warfare program who helped debrief Dr. Alibek after his defection in 1992, said many of the book's assertions were consistent with what Dr. Alibek had told American officials in secret sessions at the time. He called the information that Dr. Alibek had provided ''critical'' to Washington's understanding of the Soviet program.