Three days into a four day visit with Fidel Castro that ends today, Sen. Frank Church was beginning to sag visibly.

By noon yesterday, Castro had taken him to a public housing project, a rum distillery and a beachside youth camp where thousands of wet, sandy swimmers had scrambled out of the water at the sight of their leader, smothering him in a crush of damp adulation.

While Church - who was virtually ignored by the crowd except for an occasional youthful chant for Fidel to "be tough with the Yankees" - was tiring, Castro seemed to drink energy form the hear and pandemonium.

The atmosphere created by Castro's mere presence is a combination of an American political campaign and, for those familiar with classic Latin political frenzies, a scene right out of the dictator mold of the late Juan Peron of Argentina.

El Presidente, mythical, magnanimous, with uniformed guards at his side, strides boldly into his flock, chucking chins, patting heads and kissing babies. Women scream, straining to touch him with hands they swear they will never wash again.

Castro's aides made no effort to hold back the crowds or to protect him form endless touching, conversation and questions. If you can catch his attention, Castro puts himself at your mercy.

With foreign journalists trailing the tour yesterday. Castro was often more like a candidate than an established leader. He posed for endless pictures, patiently answered even the most frivolous questions, joked, charmed, and repeatedly asked if everyone was happy.

Most of the U.S. Senate, Church commented wryly, could probably stand some lessons from Castro on how to deal with the press.

He handed out bottles of rum like water, tried to get everyone drunk on local firewater and scolded the reporters for worrying about deadlines instead of sitting down to eat with him at a rural school lunchroom.

Apparently because no one else was willing to exercise authority in his presence, Castro tock personal charge of what turned out to be an unsuccessful effort to supply some long-distance press calls to the United States from his brother Ramon's cattle farm.

It was obvious from the start that the church entourage was getting the red-carpet treatment - virtually unlimited time with Castro for two days; a steady flow of gifts, including boxes of El Comandante's specially made (not for sale) cigars; a personally escorted trip to the Bay of Pigs.

Church has not been one of the most vocal Senate proponents of normalizing relations with Cuba.In fact, as Church himself pointed out, despite his heading the investigative committee that discovered CIA plots against the Cubans, the isue of close Cuba ties is not a popular one in his conservative Idaho constituency.

Asked why Church had been singled out for invitation, Castro described the senator as an "important, courageous politician . . . with a lot of personal prestige in the United States." Saying he was "happy" to have met Church, Castro lauded him as being "capable, serious and intellectual . . . and a man you can talk to."

Castro denied that the numerous previous U.S. Congressional visits here meant he is out to collect a legislative majority in Washington.

"It's a question of having influence in the Senate," he said. "All of the visits have been under different circumstances. Personally, you could say that I'm always interested in U.S. policy and a better opportunity" to know the United States.

"You can't forget that a real abyss has existed" between the two countries, he said. Besides, Castro added, "I like to talk."