Public threats by Reagan administration officials to strike militarily at Cuba have led this Caribbean island to reconsider over the past four years the understanding that resolved the October 1962 missile crisis by ruling out the stationing of offensive Soviet weapons in Cuba in return for a no-invasion pledge from the United States.

Saying that Cuba would have no choice but to seek every means it can to protect itself "if this contract is not honored," Cuban President Fidel Castro indicated in his interview with The Washington Post that the improvement in relations he hopes for with Washington will not be made at the expense of the privileged position the Soviet Union has built up in Cuba through extensive military and economic aid.

Castro also cast new light on the 1962 missile crisis by confirming that Soviet troops manning antiaircraft missile batteries shot down an American U2 reconnaissance aircraft at the height of the confrontation without getting specific clearance from Castro or other Cuban authorities.

"I did not have the honor of shooting down the spy plane," Castro said in response to a question about assertions that he had personally participated in the Oct. 27 incident. He said that he had given general orders to Cuban antiaircraft artillery units to fire on low-flying U.S. aircraft, since they could be preparing to hit Cuban targets.

"We did not run the ground-to-air missiles. There were Soviet personnel running the battery" that downed the U2, Castro acknowledged, adding quickly, "but it is our responsibility. We gave the order to fire on low-flying aircraft."

Uncertain at the time of exactly how the U2 had been downed and striving in the final hours of the crisis to reach agreement with Soviet premier Nikita Khrushchev, the Kennedy administration did not call attention to the probable Soviet role in the incident.

In a separate conversation, Cuban Vice President Carlos Rafael Rodriguez said that the Soviet military action had not created a problem between Cuba and the Soviet Union. "I don't think there were any negative consequences for the military personnel who were involved."

But Rodriguez confirmed that tensions had been created "by the way the problem was solved" when the Soviet Union, without even consulting Castro, agreed to pull medium-range ballistic missiles out of Cuba in return for the U.S. pledge not to invade Cuba.

The Soviet Union, which reportedly has about 5,000 troops including a combat brigade in Cuba today, provides Castro with an estimated $4 billion a year in economic aid, or about half the total Soviet aid for the world.

Cuban officials indicated that the tough rhetoric of former secretary of state Alexander M. Haig Jr. and others had forced them to conclude that the United States no longer felt bound by the pact. Castro did not say whether he had raised the subject of the understanding with Soviet officials, or whether he would seek offensive Soviet weapons in such a situation.

But Castro emphatically rejected any suggestion that improving relations with Washington would affect his general foreign policies. "The improvement of relationships with the United States will never happen if it is on the basis that we give up moral principles."