WASHINGTON - The Bush administration accused Cuba on Monday of maintaining an offensive biological warfare program and said the island's threat to U.S. security has not been stressed enough.

The accusations marked the first time that public officials in Washington have flatly asserted that Cuba is developing deadly biological agents and might be transferring the know-how to other states wishing to harm the United States.

''The United States believes that Cuba has at least a limited offensive biological warfare research and development effort,'' Undersecretary of State John Bolton said in a speech to the Heritage Foundation, a conservative think tank in Washington.

Bolton, one of the administration's senior experts on arms proliferation and terrorism, said Washington has evidence that Cuba is providing dual-use technology -- that could be used either for peaceful purposes or for lethal weapons-production -- to hostile nations.

''We call on Cuba to cease all biological weapons-applicable cooperation with rogue states,'' Bolton said.

He did not identify the nations that may be receiving the Cuban biotechnology, although he mentioned that Cuban leader Fidel Castro visited Iran, Syria and Libya last year.

''I wish I could go into a lot more detail,'' Bolton said in response to a question.

He said he was revealing Cuba's capacity for the first time because U.S. officials have strong confidence in the evidence they have collected.

''For reasons and concerns with sources of that information, and our ability to continue to learn about Cuba's activities and the other activities of rogue states, I'm not at liberty to go beyond what I've said,'' Bolton said.

Bolton's accusations were hailed by Cuban-American groups, who urge the White House to embrace a position stating that Castro's regime represents a danger to the United States.

Since the collapse of the Soviet Union, many U.S. citizens no longer view Cuba as a threat.

`AMPLE EVIDENCE'

''For decades there has been ample evidence pointing toward the Castro regime's determination to develop and produce biological weapons,'' said Jorge Mas Santos, chairman of the Cuban American National Foundation.

''Too often in the past, however, this fact was swept under the rug by those eager to downplay Castro's longtime hatred of the United States,'' he went on.

The State Department lists Cuba as one of seven nations that sponsor international terrorism, largely because of the presence of foreigners wanted on terrorism charges in their home countries, including Puerto Rican radicals, other wanted Americans, and members of the Basque separatist organization ETA.

VOICED SKEPTICISM

Under the Clinton administration, officials voiced skepticism at reports that Cuba might be involved in developing or stockpiling offensive biological warfare agents.

Last year, a high-level former Cuban scientist, José de la Fuente, who was once director of Cuba's Center for Genetic Engineering and Biotechnology, contended in a U.S. scientific journal that Cuba had sold dual-use technology to Iran. President Bush in his state of the union speech in January called Iran part of an ''axis of evil'' that included Iraq and North Korea.

''We know that Cuba is collaborating with other state sponsors of terror,'' Bolton said, adding that Castro ``continues to view terror as a legitimate tactic to further revolutionary objectives.''