CAMEO ONE: In this uniform of dark blazer and regimental tie, there's a ring of Ivy to him as he extols charity and voluntarism, the seeming epitome of the storied self-made, conservative American businessman.

Cameo Two: A half-buttoned tropical sports shirt exposes the paunch, his red hair flares and he brandishes a dark Cuban cigar, maybe a little full of himself, fantasizing about unlocking the world's political prisons.

These are the two visible, yet beguilingly contrapuntal sides of Bernardo Benes, the Miami banker who was the key go-between in the Cuban government's decision to free thousands of political prisoners.

President Fidel Casto announced 10 days ago that he would release 3,000 political prisoners and let them and other thousands of former prisoners and their families leave Cuba. By Castro's estimates, 50,000 Cubans or more could be affected directly.

Diplomats and politicans eventually will parse the meanings, whatever they are, of Castro's moves. But for now, his announcement stands as one of recent history's larger and more positive human-rights episodes.

One of the ironies of the story is that Bernardo Benes, who fled from Cuban communism 18 years ago, could return home by invitation to sit with Castro and negotiate over prisoners and their families.

Benes refuses to provide details of his encounters with Castro and his secret trips to Cuba, undertaken, evidently, with approval of the Carter administration.

But the little that is known suggests a story equally intriguing as anything that a Greene or a Le Carre might fictionalize in a tropical setting where East and West are at philosophical loggerheads.

"I am just not going to talk about details -- nothing until the last prisoner is out," Benes said the other day. "It is still a very sensitive situation. But I think the impact of this is going to be tremendous. It is the biggest step in liberalizing things that any Communist nation has taken since 1917."

Castro himself, surely, would not object to such a sweeping characterization. Understandably, from the first Cuban contacts with Benes, which apparently occurred in Panama in August last year, Castro had emphasized that he would not do business with any exile organizations which were actively opposing the Cuban government.

As the story finally developed, the final, formal talks in Havana in mid-November involved Castro and 75 exile representatives who generally have not been involved in anti-Castro agitation outside of Cuba.

First Contact in Panama

BENES, the nominal leader of the delegation, was in many ways the most logical man for the Castro government to approach in the beginning.

He had become respected and successful in business in Miami, he had stayed clear of the Byzantine politics that mesmerize the exile community and he had been Jimmy's Carter's 1976 campaign director for Hispanic affairs in Florida.

As Castro and Benes have emphasized, the issue of freedom for present and former prisoners had to be discussed outside of official circles -- since Cuba and the United States do not have diplomatic ties -- as a matter of Cubans dealing with Cubans.

According to sources, the first formal contact occurred when Benes, in Panama on a business trip, was approached by a Castro emissary. They apparently discussed closer relations with the United States, the prisoner question and the reunification of families separated by exile.

Other later contacts were made and, while Benes refuses to confirm the fact, it is thought that he made at least one secret trip to Cuba, probably more, with the knowledge of Washington, for further talks.

Castro, meanwhile, in meetings with visiting Americans and news reporters, dropped hints of his interest in developing some kind of mechanism for freeing political prisoners and sending them out of Cuba.

Last August, a Cuban government official went to Miami to talk further with Benes. They apparently discussed the mechanics of a massive prisoner release and ways of letting them leave Cuba.

Events thereafter moved quickly. In September Castro let it be known he was ready to act. By mid-October, 46 political prisoners and three dozen relatives were cleared to leave Cuba and Benes escorted them to Florida from Havana.

"When we met in October, Castro said he didn't believe in delays," Benes recalled. "He said the release of the 46 was to show his good faith, and while he admitted it was good for his image abroad, he indicated he thought this would be a move beneficial to all Cubans."

For his involvement, Benes has been the target of threats from exile organizations -- groups Castro describes as still waging "a holy war" against his regime -- which oppose any warming in U.S.-Cuban relations.

Benes seems undeterred. "This is a logical historical step for us to take," he said. "The price of being a Cuban with a social conscience has been very high -- even higher for a Cuban Jew, like myself -- but there is no need for political prisoners anywhere in this world... I have talked to hundreds of Cuban prisoners and their situation is a major tragedy of our generation. Castro has been responsive and it would be a shame for us not to expedite this by opening our doors to those who want to come here."

"Always Been Involved"

WHEN BENES says "us" he is taking about the United States, for he, like many another Cuban exile and beleaguered immigrant from elsewhere, has become a citizen. He doesn't care for Castro's politics, but he thinks it makes sense for the U.S. and Cuba to be friends -- it would benefit both countries.

Jack Gordon, president of Washington Federal Savings and Loan Association in Miami Beach, gave Benes a $65-a-week job as an auditor when he showed up in Florida in 1960 as an exile from Cuba.

"We gave him a job, he understood the operation and we couldn't hold him back. He was promoted to several other positions," Gordon said. "Bernardo has a very strong set of American values. He's optimistic about people and he has a very good traditional Jewish sense of obligation to the less fortunate.

"Bernardo has tried to sensitize the establishment here as to where the Spanish community was, through United Way and the Urban Coalition. He's always been involved, trying to make the Anglo community aware of what is out there."

Benes, 44, was born in Cuba; his father was a Russian, his mother Lithuanian. The elder Benes went into manufacturing and, before it was confiscated by Castro in 1960, had built an empire worth several million dollars. He left Cuba with $15,000, died in exile here in 1968.

Bernardo was sent to the United States to study. According to a family story, he quit the University of Maryland after two days, returning to Havana because the dormitory beds at College Park were "too hard."

He studied at the University of Havana, trained in law and accounting and briefly was a consultant to Castro's treasury department before leaving the country in 1960.

Less than a year after Gordon hired him, Benes had become vice president of Washington Federal. He was involved in the Alliance for Progress housing program and, in what he considers one of his proudest achievements, helped train Latin Americans who subsequently would set up 200 savings and loans associations, financing some 2 million housing units.

"Some of my friends and I had a vision," Benes said. "We wanted to start the first Cuban-American bank in the United States. We picked a corner in Little Havana, here in Miami, and 3 1/2 years ago that's where we opened it."

The Continental National Bank of Miami, with Benes as vice chairman of the board, has $32 million in deposits and appears to be thriving. "I think it's important to mention that no one owns more than 5 percent in this," Benes said.

The prisoner negotiations have cut into his time for business, but Benes thinks that is one of the prices of his citizenship. "Politically, morally, I can't see how we cannot be generous with these people. We are talking about thousands of tragedies -- we look at the numbers in absolutes and we don't realize that each of these cases is a human tragedy," he said.

Tears were welling up in Bernardo Benes' eyes by then. "Many times, I felt lonesome, but my son -- he's 19, studying at the University of Florida -- urged me to continue on. I needed that a lot. But I believed in what we were doing -- there are still some Don Quixotes in the world. I feel 50 feet tall now. After this Cuban process, I think all the political prisons of the world will loosen their locks."