Openly expressing fear of retribution, a prominent Cuban exile testified yesterday that Mafia chieftain Santo Trafficante told him in the summer of 1963 that President Kennedy would never be reelected because he was going to be "hit."

Guarded by federal marshals at his request the witness, Jose Aleman of Miami, promptly couched his story with suggestions that there might be an innocent explanation for Trafficante's remarks.

Contrary to earlier interviews, both with journalists and House Assassinations Committee investigators, Aleman said he thinks the Florida underworld leader was merely saying that Kennedy was going to be "hit" with "a lot of votes from the Republican Party."

Once the overload of syndicate gambling in Havana before Fidel Castro's rise to power in 1959, Trafficante listened stolidly to the broadcast testimony in a nearby room, waiting to be called as a witness himself.

The hearing was marked by confusin and delays. The afternoon session was held up for more than three hours by the absence of Chairman Louis Stokes (D-Ohio), who was attending a House-Senate conference at the request of the White House, and then was finally canceled when Trafficante asked to be excused until the morning.

Trafficante was summoned before the House Assassinations Committee on the same issue once before, in March 1977, but he refused to say whether he had advance knowledge of the president's assassination or to answer any other questions.

Since then, the committee ahs reportedly obtained a court order to immunize the Mafia leader and thus force him to testify or face a contempt citation.

Aleman, a gray-haired businessman who once fought against the Batista government and then against Castro's, did not change his account of the conversation with Trafficante, only his interpretation of it. But the shift plainly chagrined committee members who emphasized that it was the first time he had ever indicated he thought Trafficante might have been alluding to anything but the president's murder.

The Washington Post, in an article by journalist-George Crile III, reported two years ago on the long discussion Aleman had with Trafficante in Aleman's Miami Beach motel.

According to the 1976 account, Trafficante complained of the Kennedy's especially their campaign against Teamsters union leader James R. Hoffa and said the president would "get what is coming to him."

Yesterday Aleman said that Trafficante also said at one point "You see this man [Kennedy] he's not going to be reelected . . . There's no doubt about it."

Aleman said he disagreed telling Trafficante that Kennedy "has a lot of Democrats backing him and so far . . . I don't see anything [suggesting] that he's not going to be reelected."

At that, Aleman told the committee, Trafficante replied: "You don't understand me. He's going to be hit."

According to committee staff lawyer Andrew Purdy's account of a 1977 interview with Aleman in Miami, "Aleman said he was given the distinct impression that Hoffa was to be principally involved in the elimination of Kennedy."

According to Purdy's memo, Aleman said he even had a bet with another Cuban exile, George Nobregas, about whether Kennedy would be assassinated Nobregas had first put Aleman in touch with Trafficante, reportedly to help Aleman obtain a Teamsters Union loan, and was present at the meeting when Trafficante made his prediction.

Testifying yesterday, however, Aleman insisted that "I didn't have any idea at that moment" what Trafficants meant by the word "hit."

"I just took it as somebody saying something like, you know, he's talking a lot of foolishness."

In any case, Aleman made plain that he is still "very much worried and very much concerned about my safety." He repeatedly told the committee of his belief that Castro's secret police agency is actually in cahoots with the underworld and profits from the bolita racket in Florida.

"Santo Trafficante, I believe, has a lot of connections with the regime of Fidel Castro," Aleman asserted. At another point, he said, "I still believe that the DGI [the Cuban secret police] and Santo Trafficante will try to do something to me. There's no doubt about it."