Sen. Bob Graham of Florida, who chairs the Senate Intelligence Committee, said he believes the charge may blunt congressional efforts to relax the U.S. embargo of Cuba.
U.S. intelligence agencies declassified secret information to allow John Bolton, a State Department undersecretary for arms control, to make his public accusation against Cuba in a speech Monday, officials said. The assessment was not based on new findings, they added.
The Cuban government, through its spokesman at the Cuban Interests Section in Washington, has denied Bolton's charges.
''I was surprised, frankly, at what Mr. Bolton said,'' Sen. Graham told a conference of business leaders. ``We've known that Cuba, with its large pharmaceutical industry, had had the capability to develop chemical and biological weapons of mass destruction. . . . But this is the first confirmation that those actually matured into potentially militarily usable weapons.''
Some observers of U.S. policy toward Cuba said Bolton's unexpected accusation is giving them pause.
''I must say that I was sort of shocked,'' said retired Army Gen. Barry McCaffrey, a former White House drug policy director who recently returned from Cuba, where he met with Fidel Castro, and has advocated greater cooperation with the island. McCaffrey said Bolton's stature gives credence to the new charge.
Bolton said that U.S. officials believe ''that Cuba has at least a limited offensive biological warfare research and development effort'' underway and might be transferring the know-how to other countries.
''I'd be hard-pressed to think that he'd make it up,'' McCaffrey said.
Some voiced contentment that their long-standing concerns about Cuba have been given credence.
''I am happy to see that the administration has finally come forth with an acknowledgement of Cuba's capabilities,'' said Rep. Bob Menendez, a Cuban-American Democrat from New Jersey. ``Cuba's biotechnology industry is not just for medical reasons. . . . I think they could be making a variety of things, from anthrax to smallpox to other agents.''
Advocates of relaxing tensions with Cuba scoffed at Bolton's charges.
''Where's the evidence?'' asked William Delahunt, D-Mass., who is a leader of the Cuban Working Group, an informal congressional bloc opposed to the embargo. ``Accepting what they have to say as fact is high risk.''
His Republican counterpart in the bipartisan bloc, Rep. Jeff Flake of Arizona, said he did not doubt that Cuba may be working in devious warfare capabilities but that he'll continue to push for all U.S. citizens to be able to visit the island without breaking U.S. law.
In a sense, Bolton was returning to familiar ground with his speech at the Heritage Foundation. A man of strong views, Bolton was an assistant attorney general under Reagan. Later he was a senior vice president at the American Enterprise Institute, another conservative think tank.
Both Bolton and Otto Reich, assistant secretary of state for the Western Hemisphere, asked intelligence agencies to declassify information that would permit the announcement on Cuba, a State Department official said, asking to remain anonymous.
Arms control expert Milton Leitenberg, a senior research scholar at the University of Maryland, suggested that politics, more than concrete data, may have played a role in Bolton's accusation.
''I'm skeptical,'' said Leitenberg. ''Bolton is a shooter from the hip.'' Leitenberg said the likelihood of new information emerging recently that would implicate Cuba ''is probably small.'' He said he believes the Bush administration may have looked again at intelligence data and decided ``to push the chess piece over the line.''
Suspicions about Cuba center on the massive Center for Genetic Engineering and Biotechnology, a Havana installation inaugurated in 1986. It has received more than $1 billion of funding from the Castro government.
One of its top scientists, José de la Fuente, who defected in 1999 and is now at Oklahoma State University, said scientists at the sophisticated facilities have done ground-breaking research in recombinant genetic engineering, leading to a hepatitis B vaccine and a clot-busting drug, streptokinase, used against strokes.
''I heard no account of any effort for developing biological weapons in Cuba,'' said de la Fuente, who oversaw some 350 scientists as the center's research and development chief.
More worrisome, de la Fuente said, is Cuba's transfer of recombinant technology to Iran, which has eagerly sought help from the Castro regime since the early 1990s. ''Once that technology gets transferred, there's no control. The Iranians can use that technology for what they want,'' he said.
A U.S. molecular biologist and close friend of de la Fuente, Harvey Bialy, who now teaches in Mexico, said he has spent long periods in Cuban genetic engineering labs and never ''heard a whisper'' about an offensive biological program.
''What they [the Cubans] are doing is much worse. They sold to Iran all the things that Bolton said Cuba is doing,'' said Bialy, the former editor of the Nature Biotechnology academic journal. ``What is going on in Iran is the most serious bioterrorist threat to the United States at this time.''