When John Glenn lifted off into space in a Mercury capsule on Feb. 20, 1962, military planners at the Pentagon were thinking of blaming Fidel Castro if the astronaut failed to come down again.

The proposal was called Operation Dirty Trick and, according to long-secret documents made public yesterday, the idea was "to provide irrevocable proof that, should the MERCURY manned orbit flight fail, the fault lies with the Communists et al Cuba." This could be accomplished, the planners suggested in a Feb. 2, 1962, memo, "by manufacturing various pieces of evidence which would prove electronic interference on the part of the Cubans."

Glenn, of course, returned safely after becoming the first American to orbit Earth. But the memo, addressed to Air Force Brig. Gen. Edward G. Lansdale, head of Operation Mongoose, an elaborate scheme aimed at promoting revolt in Cuba, was full of other suggestions, some quite zany.

There was, for instance, Operation Good Time, which would have fabricated a photograph of "an obese Castro with two beauties in any situation desired" near "a table brimming over with the most delectable Cuban food," accompanied by the caption, "My ration is different."

"This should put even a Commie dictator in the proper perspective with the underlying masses," the memo said.

The covert action proposals were among 1,500 pages of previously classified records made public yesterday by the Assassination Records Review Board, a small agency overseeing the release of records related to the 1963 assassination of President John F. Kennedy.

"It's our sense that the assassination was part of a larger set of issues," said board member Anna Nelson. "What we're trying to do is provide context." She noted, for example, that there have been conflicting reports about whether accused assassin Lee Harvey Oswald was pro-Castro or anti-Castro and whether he might have been motivated by U.S. policies toward Cuba.

After the failure of the Bay of Pigs invasion in mid-April 1961, Kennedy convened a meeting of the National Security Council to talk about what to do next about Cuba. According to a memo for the record that appeared to contain exact quotes from the April 22, 1961, session, the president said guerrilla operations should be discontinued, but asked "whether we should form a Cuban Foreign Legion, trained as a volunteer force."

CIA Director Allen Dulles said that if this were done, "it should be done overtly."

Secretary of State Dean Rusk suggested that anti-Castro Cubans could simply be enlisted in the Army, but Kennedy said they did not want to enlist, but "to be trained for the overthrow of Castro."

One of the items assigned for study "on an urgent basis" in the wake of the Bay of Pigs fiasco was what the United States would do if faced with several contingencies, including "establishment of a Soviet missile base" in Cuba. The State Department was told to study the matter. The discovery of Soviet missiles on Cuba in the fall of 1962 provoked one of the most tense episodes of the Cold War.

At another NSC meeting on May 5, 1961, the records show, "it was agreed that U.S. policy should aim at the downfall of Castro." At the Pentagon, one contingency plan followed another.

However, other assessments suggested that overthrowing Castro would not be easy. A CIA report in April 1962 cited "probable reactions to a U.S. military intervention in Cuba." It warned that Castro had made extensive preparations to resist and though some Cubans would welcome the U.S. military, "at least as many more would regard it as designed to reimpose upon the Cuban people the yoke of Yankee imperialism.' " As a result, the CIA said, "a prolonged U.S. military occupation of Cuba would probably be necessary."

In March 1963, the chairman of the Joint Chiefs of Staff, Gen. Maxwell D. Taylor, asked for a report on what could be done "to plan and incite a revolt in Cuba." Because of past difficulties in contriving "a timed uprising," he said consideration should be given to "engineering an incident as a cause for invasion."

The Joint Chiefs' intelligence staff suggested using MiG-type aircraft flown by U.S. pilots to harass Cuban civil aviation or to attack a U.S. military plane. Another option: creating "well-coordinated incidents . . . in and around Guantanamo" supposedly done by "a hostile Cuban force to establish a credible attack against the U.S. Naval base."

Such pretexts had been suggested to Kennedy in March 1962 and, according to a memo record, he said "bluntly" that he would not discuss the use of military force in light of dangers then pending in Berlin and other places where Soviet and U.S. forces were potentially in direct confrontation.

Kennedy's assassination on Nov. 22, 1963, left the new president, Lyndon B. Johnson, unenthusiastic about "high-risk actions" involving sabotage and harassment. A memo summarizing a high-level Dec. 19, 1963, meeting on Cuba stated that Johnson was "most interested in economic denial actions." But Johnson said he did not want to jeopardize chances of getting the Organization of American States to back actions against Cuba. He said he also wanted to continue to work for "further reductions in Soviet military personnel" on the island.