The priest said the mass in Spanish and the congregation packing the pews sang a beautiful song in Spanish. It was a special experience for one man in a front-row pew who did not sing along. Not only did he not know Spanish. He wasn't even Catholic.

Protestant Ronald Reagan found his way to Little Havana's Sts. Peter and Paul Church not for any new-found interest in comparative religion. He was simply playing Ethnic Politics, wooing the Cuban vote, a strong voice in Dade County Republican primary politics.

As Reagan moved through the crowd after services, there were cries of "Viva Reagan" and "Reagan, Si" -- with his name universally pronounced Reeegan. With their Bay of Pigs memories, their hatred of Fidel Castro and their fierce anticommunism, Cuban refugees have long embraced Reagan's military might-is-right stance. Reagan has been their man in Little Havana.

The statistics tell the story of why Reagan, and more recently George Bush, both ostentatiously courted the Latin vote for today's primary. Cubans make up one-third of Dade's registered Republicans, and they generally vote in large numbers. Primaries belong to true believers, and the Dade County Cubans are the truest of believers. Four years ago, as most of Florida went for Ford, the heavy Latin vote gave Reagan a strong Dade County victory over the incumbent president, who was seen as soft on Castro.

As Cubans increasingly give up their dreams of sometime returning to Cuba, they are more and more becoming American citizens and are registering to vote.Six years ago, only 36,000 were registered in Dade County.Today there are more than 103,000. In an overwhelmingly Democratic county, they are a last Republican stronghold, with 40 percent Republican and another 12 percent Independent.

As they become more sophisticated to the workings of American politics, they are becoming a Hispanic political power base to match their numbers. This year, for the first time, Latins became the leading minority group, ahead of blacks, in Dade County. And, for the first time, they have a three-man majority on Miami's five-man city council. Fiesta

Out from the West came another gunslinger on Sunday -- the Connecticut Yankee transplanted to Houston, George Bush. Into the fray he came, shortly after Reagan had walked the very same blocks. It was the Calle Ocho festival, a sort of Cuban Mardi Gras, and Eighth Street in Little Havana was wall-to-wall Spanish. Some 300,000 Latinos strolled the street, shouting greetings in Spanish, starting impromptu dances as bands belted out salsa rhythms on every corner. Beer and pina coladas went down fast in the broiling sun.

Suddenly a phalanx of blue Bush signs, Secret Service, national press and Bush supporters moved onto the street. Somewhere in the middle of it all was George Bush.

Having been crushed by Reagan in South Carolina. Bush was running especially hard. When asked in a shouting mob of reporters how important he considers the Cuban vote, Bush said, a little testily, "Very, very important. That's why I'm here."

He struggled through the mob, and he didn't look very presidential, what with the sweat dripping and his halting attempts at Spanish. He wore the popular Latin guayabera short-sleeved shirt. As one Cuban supporter grabbed a mike at one grandstand, Bush reached for it and told the crowd what they wanted to hear. Five years ago, anyone connected with the CIA was running for cover. Today, and especially in this crowd, the former CIA director was thunderously cheered as he said, "I am for a strong military and for a strong CIA. I will not be taken by Fidel Castro!"

A few minutes later it was clear that Bush also had no desire to be taken by the crowd. Ducking into the Centro Vasco restaurant, the Secret Servicemen leaping over greenery to keep up as Bush shouted to no one in particular, "Let's get in here before we get knocked down." Dominoes and Debacle

It is Saturday afternoon and the American Club in Miami -- the same Havana club started by rich American businessmen and transplanted to America after Castro's takeover -- is doing a brisk business. In one corner elderly Cuban men play dominoes while young, wealthy Cuban Kiwanians, sponsors of the Calle Ocho festival, are stringing confetti for that night's opening party. Raucous Spanish emerges from a crowd of five men at the bar, playing mentirosa, or "the liar" in English. It is a dice game, and as one slams down his dice in a cup and shouts out the number, others challenge him as to whether he is bluffing or not.

In this crowd of affluent businessmen, there are many success stories to match the gold so much in evidence in chains around their necks, and rings on their fingers. These were the upper-and middle-class people who 20 years ago fled Castro's Cuba with, as one said, "nothing but our backgrounds."

Guido Echevarria, a prosperous real-estate developer, smokes his long cigar, sips his brandy and sits with his wife and two sons. "I knew Castro. We went to law school together. But he was with the agitator group." Echevarria, on the other hand, graduated to become in charge of Batista's security forces. "I came to this country with $19 and I was 25 years old. I am 46 now. I worked at anything. A busboy at the Americana Hotel, I worked at a funeral home. Then I was contacted by the CIA. I was in the Bay of Pigs. My father, too. He spent 20 months in prison. I was able to escape."

Like many Cubans, Echevarria blames John F. Kennedy, not the CIA for bungling the 1961 Bay of Pigs invasion. Carter's recent attempts to reach some sort of easing of relations with Castro are "not only treason to the Cuban people but also treason to all democratic people, Mr. Carter is talking about the human rights -- but his policy is against the right humans."

Echevarria explodes about the American economy and inflation and says that we are seen as weak to the world. "I travel a lot in South America and Central America, and we are like second-class people. America means 'funny.' It means nothing now. The best thing is for Carter to resign. I am Republican and the best man now is Reagan. He has been accused of being an old man. But what about De Gaulle? He saved France from communism."

Across the bar is another Bay of Pigs survivor, Raul Gonzalez. "I came over (to the United States from Cuba) with one idea in mind. To go with the invasion." He spent two years in prison. "How was I treated?" Gonzalez laughs. "Badly." He returned to Miami when "the United States paid that famous ransom." Gonzalez blames Kennedy, the "blindness of his intelligence people" and the media for the Bay of Pigs "debacle." "A right-wing dictator the media calls a murderer -- but a left-wing murderer like Castro is called a revolutionary." (He is still undecided between Reagan and Bush.) Still Gonzalez is one of the few Republicans who see some merit in trying to work out relations with Castro. While Cuban Democrats are more inclined to that view, it is still highly unpopular with Cuban Republicans.

"I think maybe something could be accomplished," says Gonzalez. "It's like having someone in the family who is very sick and you go to the doctor and nothing can be done and then someone says there is this voodoo person or some such thing that could help. You're going to do it because nothing else works. Nothing has worked for 20 years."

The most effective antidote to Castroi's Cuba says Gonzalez, would be if Cuban Americans did return to Cuba to visit. "They left penniless and now they are properous. The Cubans back home would start to say, 'How come my sister has three homes and two cars and I'm staying and starving in Cuba?'"

The epitome of the success Gonzalez speaks of is Luis Botifoll, standing nearby in an expensive striped business suit. A lawyer when he lived in Havana, Botifoll was "not able to take out anything." After a few years struggling at odd jobs, he moved up the ladder and is now chairman of the Republic National Bank, the first Latin bank started in Florida. There are now many. His bank does more than $250 million a year in deposits. Reagan "is the best." Not only because he is strong on Cuba, says Botifoll, but brings up what is the secondary concern of many Cubans, inflation. "Carter should not run this country. He should be a priest, but not a president."

A member of the national press attempts to pin Reagan down on what he means by harassment, but Reagan turns vague. He was even more vague when a Spanish-speaking journalist asked him what specifically he would do to end the problems with Cuba. "I don't know that I can answer that question specifically. My policy (toward Cuba) would be based on my longtime view that captive nations must once again know freedom."

But the message, vague in detail or not, is going over among the Cuban Republicans. The fervor of a two-decade-old fight is in the voice of one middle-aged man who shouts out when Reagan solemnly declares of cuba, "Our country still has an obligation." The man, standing near the Bay of Pigs monument, exclaims, "We are ready again, anytime!"

Viva Republican politics in Little Havana.