Sen. George McGovern, fresh from a four-hour conversation with Fidel Castro in Havana, intends to push legislation to lift partially the 15-year-old U.S. trade embargo against Cuba.

McGovern told a press conference yesterday that he will meet with president Carter soon and ask him to support an amendment that would permit U.S. firms to sell food and medicine to the Caribbean island, as the first substantive step toward normal relations.

The Cuban president told the South Dakota Democrat on Saturday that Cuba will not extend its anti-hijacking agreement, which expires Friday, until the United States takes some kind of concrete steps to reopen trade.

"The embargo is the big sticking point," McGovern said, "and i don't think much is going to happen until that is lifted, at least partially."

McGovern and South Dakota's other senator, Democrat James Abourezk, led a tour of Cuba last week, in which about 70 South Dakotans visited the Communist country and a basketball team from the two state universities lost two games to the Cuban national team.

Cuba has agreed to return the visit by sending its basketball team to South Dakota next fall, assuming the State Department approves visas, McGovern announced. He hopes the Cubans will play two games in his state, then play several more with nationally-ranked college in the Midwest and West, such as Marquette and UCLA.

The senator also made progress in arranging U.S.-Cuban competition in baseball. Castro has accepted the idea of a U.S. all-star team playing Cuban all-star in Havana, McGovern said, and Major League Baseball Commissioner Bowie Kuhn told McGovern yesterday that such an exhibition could probably be arranged next fall or the following spring.

After the basketball diplomacy, McGovern remained in Havana for his meeting with Castro, whom he first met two years ago in a lengthy conversation about resuming U.S.-Cuban relations. As chairman of the Foreign Relations Subcommittee on International Operations, McGovern intends to attach an amendment to this year's State Department authorization which would remove the embargo on food and medicine.

The embargo, McGovern said, "never did make any sense. It only made Cuba more dependent on the Soviet Union and elminated any influence we might have. It was an entirely irrational act on our part."

Castro, indeed, told McGovern that the "political risk" of removing the trade embargo is probably greater for Cuba because trade relations with the United States might then "impose certain political constraints" on Cuba's foreign-policy initiatives.

"Cuba, he noted, is a poor, developing nation with much to gain from commercial relations with the U.S," McGovern said. "And his point was that, once such economic relations had been created. Cuba would have no choice but to consider the value of that relationship as it set its other policies."

Cuba's military intervention in Angola has been one of the main aggravations tot he U.S. government and has probably slowed down the diplomatic process aimed at resuming normal relations. McGovern said the Cuban leader assured him that, contrary to some international reports, there are no Cuban troops involved in Zaire or Uganda and there is no intention to become involved there.

McGovern said Castro renewed his complaint about the terrorist bombing of a Cuban airliner last October in which 73 people were killed - which the Cuba blame on the Central Intelligence Agency. McGovern said he told Castro he was certain that the bombing was not the work of the CIA, but it may have been done by anti-Castro Cubans who were once associated with the CIA.

"To him, it was clear, this was a distinction without a difference," McGovern said.