Cuban President Fidel Castro has released a 28-year-old letter that appears to put to rest the notion that he favored a pre-emptive nuclear attack against the United States during the Cuban missile crisis.

Instead, Castro said in his letter to Soviet leader Nikita Khrushchev that the Soviets should exercise the nuclear option only if the United States invaded Cuba for the purpose of occupying it.Two years ago, at a Moscow conference of American, Soviet and Cuban participants in the 1962 crisis, Khrushchev's son, Sergei, was reported to have told some American delegates that Castro had recommended an immediate nuclear strike against the United States at the height of the crisis.

The Castro letter, dated Oct. 26, 1962, and reprinted in a Communist Party newspaper in Havana recently, showed that the Cuban leader believed U.S. military action was likely within 24 to 72 hours.

Castro said he saw two options: an air attack against specific targets - presumably the Soviet nuclear facilities in Cuba that had provoked the crisis - and, less likely, an outright U.S. invasion of Cuba.

Castro warned that the Soviets could be the target of a U.S. nuclear strike if the United States were able to invade and occupy the island.