Nearly two decades after his face first graced American television screens, initially as a bearded guerrilla oddity and later as an imminent threat to the Free World, Fidel Castro has again become U.S. media star.

Since the beginning of this year. Castro has appeared on two prime-time network interviews. He has been host to several U.S. congressional groups with large press entourages, a U.S. college basketball team and 52 Minnesota businessmen.

As a result the president of Cuba, a country with which the United States has neither diplomatic nor trade relations, has had probably more coverage than any U.S. official short of President Carter an da few' members of his Cabinet, and almost certainly more than any other head of state.

Though what appears to be a carefully planned public relations campaign directed by Havana, the Cuban bear is slocly transforming his U.S. image into that of an engaging Teddy.

No one knows the value of that kind of free public relations better than Fidel Castro. Playing official visitors and reporters like violins, he has left most of them with the impression that small integrity, beloved by his people and the victim of undignified U.S. bullying, but also someone who is fun to pal around with.

Many Cuba-watchers believe that Castro is pulling a Cartersque end-run around Carter, who has said he will not consider normalizing relations with Cuba until several conditions are met, and around conservative U.S. legislators who oppose lifting the 15-year-old embargo on trade with Cuba.

In Carter fashion, Castro is taking his case to the American people.

Castro's most successful gambits have been with the visits of carefully selected American legislators - beginning nearly three years ago with Sen. Jacob Javits (R-N.Y.) and Claiborne Pell (D-R.I.). Having met with Castro one day after he delivered one of his harshest anti-American speeches on record, they returned to describe him, in news stories published throughout the world, as "frank, warm and friendly . . . interested in working toward better relations."

Among the most successful visits were those of Sens. George McGovern (D-S.D.) and Frank Church (D-lowa) - two former presidential candidates whose trips to Cuba put them back on the front pages. Both were doubtless chosen for special treatment by Castro in part because of their liberal foreign policy views and their fame, in the United States.

Both brought large press contingents to Cuba, McGovern in 1975 and last spring, and Church on a four-day visit earlier this month. Both were treated to the Castro charm, getting personally escorted tours of the island and a barrage of questions that showed extensive briefing and a flattering level of personal interest. Castro's inquiries ranged from McGovern's record as a World War II bomber pilot to the quality of potatoes grown in Church's Idaho.

"I've never met with any chief of state who had such an obvious interest in Idaho," Church marveled. As for a possible Carter-Castro encounter, Church said he thought "they'd hit it off."

What is important about such serendipitous reactions, however, is not necessarily that Frank Church "found a friend" in Cuba, but that his trip to the veiled island gave him, and other returning officials, an opportunity to espouse anti-embargo, pro-normalization views to a national media audience.

McGovern, in a long article in the New York Times Magazine last March, described Castro as "soft-spoken, wry, sensitive, sometimes witty, sometimes slightly ill at ease." McGovern wrote, "I frankly liked him and so did the rest of my party."

There is no justification, McGovern added, for "continuing either the trade embargo or the diplomatic isolation of Cuba."

Four days after he retuned from Cuba bearing the diplomatic plum of Castro's agreement to release the Cuban families of more than 80 American citizens, Church told the country on ABC's "Issues and Answers" that it is up to the United States to make the next concession toward normalized Cuban-American relations.

Frank Church obviously has more leeway to say nice things about Cuba than Secretary of State Cyrus Vance does. While the non-official pronouncements do not carry the weight of U.S. policy, however, they are widely watched and read by the American public, a fact which is not lost an Castro.

The reporters themselves have given Castro some of his best chances to endear himself and Cuba to Americans. Correspondents, accustomed to trailing diplomatic meetings with little hope of informal contact with the participants, find Castro available, accessible and always ready to talk. They rarely neglect to file at least one human-interest piece about friendly Fidel.

In a major media coup, ABC's Barbara Walters earlier this year was treated to a week of personal attention by Castro, including an escorted trip to the Bay of Pigs invasion site that, as shown on television during an hour-long interview, made that symbolic part of American history seem little more than a nice, palm-shaded beach.

Apparently Castro's accessibility does not extend to resident foreign reporters in Cuba, who find it nearly impossible to obtain an interview with Castro or any other high Cuban official. It is reserved for special visitors with a large, guaranteed American audience.

Although President Carter has said that relations will not be normalized until Castro pull his troops out of Africa and releases political prisoners, an April Gallup poll showed that 53 per cent of the American people feel that diplomatic relations should be reestablished.