Officials say intelligence analysts have long focused on Cuba partly because its huge investment in biotechnology has produced what is regarded as Latin America's most sophisticated biomedical capabilities.

According to a report on Cuba and germ weapons posted on the Web site of the Washington-based Federation of American Scientists, Mr. Castro intensified concern among American officials about Cuba's germ-related activities in February 1997. He compared the United States to a dragon and Cuba to a lamb, warning that the dragon would find its meal poisoned if it tried to eat the lamb.

Cuba, in fact, is one of the few developing nations to play a significant role in drug and biotechnology activities. The Web posting calls Cuba's effort ''unmatched elsewhere in the developing world.''

Cuban biotechnological research is far advanced in genetic engineering. That has enabled Cuba to make new vaccines for its comprehensive immunization program, which is widely admired by scientists and physicians. Cuba also makes drugs like recombinant streptokinase, the ''clot buster'' for heart attack victims. In 1995 Cuba sold $125 million worth of these products, primarily to other developing countries, especially to former Soviet states.

In a breakthrough for Cuba in late 1999, SmithKline Beecham, the British-American health care group, announced an agreement to test and market a new Cuban meningitis vaccine, first in Europe and eventually in the United States.

Mr. Bolton's office declined to specify what Cuban cooperative effort with another country concerned the United States most. But José de la Fuente, the former director of research at Cuba's Center for Genetic Engineering and Biotechnology, wrote in the journal Nature Biotechnology late last year that he was ''profoundly disturbed'' about Cuban sales of dual-use technology to Iran.

''No one believes that Iran is interested in these technologies for the purpose of protecting all the children in the Middle East from hepatitis,'' he wrote.