MIAMI -- One of the peculiarities of municipal politics here is that Fidel Castro is a local issue, as important to public debate as police salaries and pothole repair.

That made South African black leader Nelson Mandela controversial even before he stepped off the plane during a visit last June. Throughout his triumphal U.S. tour, Mandela committed the ultimate Miami sin of refusing to disavow his support for the Cuban president as a fellow revolutionary.

There was no official welcoming party waiting to present Mandela with the key to the city. There was no official proclamation from the Miami city commissioners. Instead, the newspapers trumpeted a letter from local officials, including Cuban-born Mayor Xavier Suarez, denouncing Mandela's remarks as "beyond reasonable comprehension."

For Miami's black leaders, the snubbing of the man who had become the source of inspiration for blacks everywhere was a deep insult. "To reject Mandela," said Johnnie McMillian, president of the local chapter of the NAACP, "is to reject us." To retaliate, black leaders launched a national boycott of Miami's convention and tourism industry, and demanded their mayor and other officials apologize.

But for five months now, despite several tortured formulations of public regret, Suarez has refused to say "I'm sorry" in a way that satisfies the black community.

Numerous attempts at mediation by civic and church leaders have been unsuccessful, and officials estimate the boycott has cost the city $12 million in business.

A dozen groups, mostly black professional associations, have canceled Miami convention plans, as has the American Civil Liberties Union and the 70,000-member National Alliance of Postal and Federal Employees.

In this poly-ethnic coastal city, as famous for its constantly simmering racial tensions as it is for its serene tropical vistas, the long-running Mandela uproar is only one of a seemingly endless series of similar controversies.

Miami -- whose nearly 400,000 urban population is 60 percent Hispanic, 15 percent black and 25 percent "Anglo" -- is one of America's most diverse and divided cities, where the endless complexities of racial and immigrant politics mean that any disagreement can become a conflagration.

Two and half weeks ago, Miami again was in the national news when frustration in a poor Puerto Rican neighborhood boiled over into the streets, where youths looted and set fires, causing an estimated $2.9 million in damage, after six Miami policemen were acquitted in the beating death of a Puerto Rican drug suspect.

Last summer, an argument between a Cuban merchant and his Haitian customer over a tailoring job on a pair of trousers quickly brought to the surface the deeper resentment Haitians feel over what they see as the Cubans' preferential refugee status.

A crowd of angry Haitians organized a protest outside the store, briefly trapping the shopkeeper inside. After three days of demonstrations, Miami police riot squads moved in with nightsticks to break up the crowd.

There are so many rivalries between new waves of immigrants from war-torn Central American countries and more established Cubans, so much competition between Haitians and Jamaican blacks and traditional Southern blacks, that even Miami's old hands have trouble sorting it all out.

Local pollster Robert Joffee, who measures Miami's attitudes on a variety of social, political and economic issues, said the city's hypersensitive ethnic differences come up in every poll he takes.

"The problem in Miami is that the black Caribbean immigrants consider themselves separate from other blacks. The Cubans consider themselves apart from Hispanics," he said.

Other Latins are often at odds with the Cuban-American community. When a plan was drafted to change "Little Havana" to the "Latin Quarter" to reflect a now-broader population of Hispanics from Central and South America, the Cuban Americans who settled the neighborhood 30 years ago caused a furor at City Hall.

More recently, the Cuban-American Bar Association once again killed a proposal to grant membership to other Hispanic lawyers and found itself accused of discrimination.

"Cubans get everything, we get nothing," a resident of the Puerto Rican neighborhood complained the day after the recent violence there subsided. "When the Cubans jump, they get what they want."

But the continuing standoff over the Mandela visit has set a new standard for controversy.

At stake are high-level political reputations and precious tourist dollars in a declining economy, as well as basic rights of blacks and other minorities. During the months of fruitless negotiations, nerves on both sides have been rubbed so raw that civic leaders fear the wounds may never fully heal.

Last month, organizers upped the boycott ante when they produced a video comparing Miami with Selma, Ala., in the early 1960s, a period when that city's name was synonymous with racism and violence. The video somehow found its way into the local press, and black leaders threatened to ship copies to convention groups around the country unless the mayor's apology was forthcoming.

Merrett Stierheim, chief of Miami's Convention and Visitor's Bureau, said he thinks the community is more polarized now than after Miami's brutal 1980 race riots, in which 18 people died.

Max Castro, executive director of Greater Miami United and an experienced conciliator in the city's ever-churning racial disputes, compares the effort to resolve the dispute to the myth of Sisyphus, the Greek god doomed to push a heavy stone uphill only to have it roll back again.

Sherill Hudson, chairman of the Miami Chamber of Commerce, said, "If this goes on much longer, there will be so much damage done, it will be impossible to recover." Hudson sent his own letter of apology to the boycotters when Suarez balked. They thanked him, but said they still needed to hear from the mayor.

Mediators say the impasse has held up dialogue on other important issues such as continuing black poverty and joblessness that are at the root of the Mandela dispute.

Miami's huge Cuban-American population, transplanted here as expatriates from Castro's revolution, has prospered and gained economic and political control of the city, while blacks have been mostly shut out of the entrepreneurial class. The city's main industry -- tourism -- employs few blacks at any level, with even the service jobs going to Hispanics. Mediators in the Mandela dispute say they would rather talk about these substantive issues and are perplexed that the mayor and the black leaders would prolong the antagonism by focusing on the less significant, but highly symbolic issue of the apology.

"I have never been so frustrated and exasperated," Stierheim said.

"Are expressions of pain and regret acceptable substitutes for the words, 'I'm sorry?' " asked Arthur Teitelbaum, regional director of the Anti-Defamation League of B'nai B'rith, who has worked with both sides in seeking to resolve the controversy. "The point has been made. Now what? Shall we be confounded because the boycotters have failed to obtain a coerced apology from the mayor?"

The boycott is the first time the black community has captured the city's attention so completely without violence. One black civic leader, who asked not to be named, said that a complicating factor is that the black community usually feels so estranged from Miami's political power brokers that the boycotters are savoring the moment.

"Mandela's visit was one of those special days for African Americans. We don't get many good days like that down here in Miami," said H.T. Smith, a local lawyer and one of the boycott's organizers.

"The black community sees itself as isolated. When we have problems, we don't hear leaders in the white community or Cuban community standing up and saying, 'What's happening?' An unfortunate incident like this one ignites that underlying feeling of disenfranchisement and distrust," Smith said.

As the dispute continues, the number of civic leaders who have privately advised Suarez to quietly apologize and move on, according to one negotiator, "is as long as the sandwich line in a deli."

But the strangely foreign, almost surreal, politics of Miami seem to have immobilized the mayor. The Cuban-American vote controls city elections. To a vocal bloc of this constituency, the Cold War rages on and Cuba remains the last vestige of an "evil empire."

"I don't think people fully understand the trauma in the lives of Cubans caused by Fidel Castro, who uprooted their whole life, who had many of their relatives killed, and many of their relatives put in jail for many years," said Steve Ross, a local lobbyist.

Joffee said the old-line Cuban exiles are not about to forgive anyone's favorable remarks about Castro, even South Africa's new hero.

"You wouldn't get a bunch of concentration camp survivors out on Miami Beach subscribing to a concert series where Wagner is performed," Joffee said. "It's the same kind of thing with these guys. And then, politically for the mayor, it's compounded by the macho thing. 'I dare you. I double dare you.' The average American says sometimes, 'I cave in. Big deal.' But in Latin culture, there's less magnanimity about the whole thing. The mayor said he's sorry. But he used other words."

Suarez said in an interview that the city's role in the Mandela visit had been misunderstood. Unlike Mandela's visits to other American cities, where elected officials hosted him, the South African hero came here only briefly to speak to a national labor convention. Suarez suggested that the convention organizers, who refused to open the meeting to Miami's black community, bear much of the blame for the ill will that flowed out of the visit.

Suarez declined to answer specifically questions about why he will not say he's sorry. He said he is frustrated to find himself "cast as one of the combatants rather than a negotiator or a leader who can mediate."

His latest attempt to calm the storm took place last week at City Hall, where he convened a press conference timed to air live on the evening news. Backed by a phalanx of stern-faced Cuban-American businessmen and exile leaders, with two black officials sitting beside him, he spoke to his troubled city.

"Words can barely begin to describe the pain I feel over the division which has occurred since Nelson Mandela visited this community," Suarez began. He said he was searching for a formula to "adequately express" his regret. He said that "wisdom" failed him.

Then he swiveled in his chair and repeated in Spanish to the Spanish-language station cameras.

But he did not apologize, and the first question the reporters asked afterward was why not.

"I think the text speaks for itself," Suarez explained. "It is the most sincere expression of how I feel. There isn't a heck of a lot more we could have done."

In the corner of the room, Max Castro was remembering Sisyphus's endless uphill struggle with the heavy stone.

"At one point, someone might get the rock up there and push it over the top," he said. But as he glumly watched the latest act in the saga unfold, Castro said he did not expect that to be any time soon.

Special correspondent Jon Leinwand contributed to this report.