The Bush administration believes Cuba is developing biological weapons and collaborating with pariah states that have their own germ warfare programs, State Department arms control chief John R. Bolton said yesterday.

Bolton, who offered no details when questioned, called on Cuba to stop delivering equipment and expertise that could be used for biological warfare by "rogue states." He said Cuba should honor its commitment to the Biological Weapons Convention, which prohibits the development and use of germ weapons.

The State Department considers Cuba a state sponsor of terrorism, and U.S. officials have long expressed fears that Fidel Castro's regime could use its sophisticated capabilities to manufacture toxins designed to kill. But this administration is the first to level an explicit charge.

The Cuban government made no official response to the allegation yesterday and attempts to reach officials at the Cuban Interests Section in Washington were unsuccessful. The Dallas Morning News quoted Cuban spokesman Luis Mariano Fernandez as calling Bolton's statement "ridiculous, absurd and a downright lie."

President Bush and members of his administration have taken a strong line against Castro, who has been in power for 43 years despite a U.S. economic embargo and strenuous attempts to isolate him. The administration is conducting a review of tools available to undercut Castro and foster democracy in Cuba, even as sentiment increases on Capitol Hill for greater engagement with Cuba toward the same goal.

In a speech to the Heritage Foundation, a Washington think tank, Bolton said Cuba's threat to U.S. security "often has been underplayed." He noted that then-Defense Secretary William S. Cohen warned in 1998 of Cuba's potential to produce biological agents. Bolton also said that Castro visited Iran, Syria and Libya last year. All appear on the U.S. list of terrorism sponsors.

Some administration officials, convinced that Cuba has an active germ warfare program, have been pressing to make the evidence public, but guardians of the information have worried that its release would compromise U.S. intelligence sources, according to more than one official.

The public statement followed extensive debate within the administration, these sources said, and "represents the considered judgment of this administration that there is a serious problem." Another official called the evidence of Cuban collaboration on biological weapons programs "incontrovertible."

As it happens, Bolton was not the first official to make a public statement on the subject. Carl W. Ford Jr., assistant secretary of state for intelligence and research, used identical language in March 19 congressional testimony that largely went unnoticed.