To judge from the unfurling of Cuban flags and the coffee-shop talk in sprawling Little Havana, one would have to believe that counterrevolution is nigh and Fidel Castro's days are numbered.

The heart of Miami's Cuban exile community always has throbbed to the beat of such anticipation, but the excitement this time is a little different, a little more fervent.

Anti-Castro manifestos flower on storefronts. Spanish-language radio exhorts exiles to new levels of patriotism. Rallies and marches are mounted. The 150 or so disperate exile political groups actually are talking to each other.

Much of it has been heard before, but it serves to remind that sophisticated, free-wheeling Miami is more than just a Mecca for tourists and retirees.

The city is a genuine center of international intrigue and conspiracy, with something for every discriminating buyer, seller, patriot, proselytizer and miscreant.

If it is counterrevolution and politics, you will find it here. If it is guns armaments or spy equipment, Miami can provide it. Illicit drugs from abroad come in the large economy size. Multilingual sects, alien-smuggling and the tools they require are readily available.

Events in recent weeks offer some insights into the darker reaches of the Sun Belt:

Federal customs agents seize about 100 high-powered weapons an army major from El Salvador tries to take home illegally. . . . Agents nail a New Jersey man trying to send Lebanon 250,000 rounds of illegal ammunition hidden in air conditioners.

Federal drug agents report seizing 291 tons of marijuana and 10.7 million Quaalude pills, mostly from Colombia, in the last six months . . ."Leaks" are said to abort a federal air and sea operation to trap cocain smugglers . . . An ex-mayor of suburban Hallandale is sentenced a second time for illegal dope sales.

An influx of undocumented Haitian boat people, seeking work and fleeing the duvalier regime, reaches epidemic proportions, with 1,043 showing up in the first two weeks of April . . . Haitians march through downtown demanding political asylum . . . Two smugglers are convicted in the drownings of a Haitian mother and her five children they were bringing here . . . Duvalier agents are spotted at refugee meetings.

Cuban exiles fast, march, rally, block downtown traffic for days, collect over $215,000 and 200 tons of food in support of 10,000 countrymen who seek refuge in the Peruvian Embassy in Havana . . . The 19th anniversary of the failed Bay of Pigs invasion is observed by 800 solemn exiles . . . Leaders urge exiles to ready themselves for new anti-Castro efforts.

All this is but a sample of the daily fare that confronts south Florida newspaper readers and television watchers.

Coincidences of geography and climate, the hundreds of miles of open coastline plus a large and sympathetic Spanish-speaking population make this a natural haven for the displaced and ne'er-do-wells of the Carribbean and Latin American.

Political turmoil in the Spanish-speaking countries is soon felt here. In the 1950s, ousted Venezuelan dictator Perez Jimenez and his cronies came here. Last year, the Nicaraguan revolution sent dictator Anastasio Somoza and 10,000 countrymen to this area.

And south Florida has been a launching pad for revolutions -- the most notable being the Cuban independence movement that culminated in the Spanish-American War of 1898. Cuban liberator Jose Marti did much of his scheming in Florida.

The Cuban connection continues to be South Florida's most constant engine of intrigue. More than 500,000 Cubans have come to Dade County since the Castro revolution of 1959, and many of them live in a state of perpetual political anxiety.

Their curent motivation is the rumbling of discontent, or what the exiles want to believe is discontent, rolling out of Cuba these days.

Arthur Nehrbass, special agent in charge of the FBI's Miami office, says, "There is a building fever in the Cuban community. Many feel that Castro is about to topple and a counter revolution is coming. They want to be near where the action is."

The FBI official's observation is quickly confirmed in the prosperous and vivacious Cuban neighborhood known as Little Havana, southwest of downtown.

Restaurants patrons are abuzz over the Peruvian Embassy drama in Havana, a subject that generates infinite theorizing and speculating. Reports of crop failure, animal disease and food shortages fuel the speculation about Castro's troubles.

Miami's Spanish-language radio stations provide constant news on the embassy situation, interspersed with patriotic music and virtual calls to arms. One station's campaign to have exiles honk their horns in a show of solidarity has drawn numerous complaints from Cubans who want to sleep in peace, the Federal Communications Commission's Jack May says.

Beyond honking horns and staging rallies, enough exile intrigue exists to keep several federal agencies working full tilt.

Immigration, Customs, Coast Guard, FBI and Alcohol-Tobacco-Firearms agents all have their eyes on political activists and terrorists, as well as on arms traffickers and purveyors of turpitude.

"With the Cuban immigrants, we have a counter-intelligence interest to assure that Castro hasn't shipped in agent," the Fbi's Nehrbass said. "And we are involved because of the domestic violence of organizations like Omega 7 and Alpha 66," rabid anti-Castro groups.

Customs and ATF agents monitor the arms trade, which is huge, according to Bob Nunnery special agent in charge of U.S Customs operations here.

"There is an unusually large number of gun dealers here, and a lot of the trade is legitimate with South and Central Americans," Nunnery said. "But because of politics, when they need arms, they tend to come here also."

Nunnery cited recent illicit arms purchases by people from Honduras, El Salvador, Nicaragua, Panama and Grenada -- nations all having varying degrees of political upheavel.

Among the vendors of military items are Sherwood International Export Corp., which advertise itself as one of the world's largest ordance suppliers, and Focus Scientific and Electronics, which advertises CIA equipment for sale -- infrared gunsights, electronic pistols and other necessities.

Dave Tucker, director of ATF activities, added, "There is a huge traffic in weapons. You can triple your money by selling in Central and South America. We really just touch the surface of this."

The other big intrigue, of course, is the illicit drug trade, which has spawned gang warfare here and drawn traffickers from all over. Enormous as the drug seizure statistics are, enforcement officials concede that they are fighting a losing battle -- they won't even estimate how much they miss.