HAVANA -- They came to Gustavo Arcos's house in plain daylight, dozens of them, then scores and finally hundreds, their young faces twisted with hatred and their voices strained and menacing the way people's voices get when they're in a mob.

There were men in uniform, Arcos remembers. Also schoolgirls, 13, 14, maybe 15 years old. Everyone was shouting angry slogans and the schoolgirls were yelling their heads off too, calling Arcos gusano -- worm -- and mechanically chanting vicious things, obscene things.

Fidel Castro's regime called the incident, which took place March 8, an "act of repudiation." Officials described it as a "spontaneous" outpouring of disdain for Arcos, who inside Cuba is considered an enemy of the revolution but outside Cuba is regarded as a human rights activist.

Arcos, as well as most foreign diplomats and journalists in Cuba, described it as a state-sponsored act of intimidation.

"It was an uncivilized act, like a pogrom," he says in his clear, patient voice, a teacher's voice. "Individually they were not dangerous -- I'd seen some of the kids in the neighborhood before -- but together they became irrational."

While the incident may have been the most blatant act of hostility against Arcos recently, it wasn't the only one. In June, Arcos was again the target of a chorus of criticism -- this time from Miami's most rabidly anti-Castro Cuban exiles. His offense: to suggest that all Cubans, including Castro's government and the exiles, engage in a national dialogue on the country's future, a "truce to search for peaceful agreements."

In an era of global reconciliation, Arcos's idea might have seemed timely. But in the hothouse of exile politics, where Castro is reviled and dialogue with him is unthinkable for many Cubans, the effect was explosive. The Miami Herald announced on the front page last week that "Cuban Miami was plunged into a heated debate the likes of which it hasn't seen in 31 years."

Armando Valladares, the U.S. ambassador to the United Nations Human Rights Commission and a former political prisoner in Cuba, called Arcos's proposal treasonous. Other, more moderate exiles lauded Arcos for his courageous defense of democracy and human rights in Cuba.

For exiles in Miami, Arcos and his idea have become the defining political standard: Where you stand on Arcos is where you stand on Cuba.

The house where Arcos lives, where the mob gathered and raised its voice that day in March, resembles so many homes in Havana -- a crumbling old mansion untouched by maintenance for so many years that you have to look closely and imagine hard to see its former grandeur.

The squeaky front door opens onto an airy foyer with a tile floor and hard, simple chairs where visitors sit and wait for Arcos or his wife to come downstairs to receive them.

A handsome man with smooth skin and close-cropped, graying hair, Arcos descends the stairs favoring his left leg. At 63, he is even-tempered and methodical, not harsh but a little humorless. In his quiet speech and intent gaze, there's barely a hint of the episodes of suffering that have marked his life: the collapse of his youthful vision for Cuba; the two terms in prison; the teenage son who lapsed into a coma after a motorcycle crash and later died; and, of course, the famous limp.

It was in 1953 when Arcos, fighting at Fidel Castro's side, took a bullet in his right leg from a Springfield rifle in Castro's fabled attack at the Moncada Barracks, the daredevil failed opening strike against the dictatorship of Fulgencio Batista.

Bleeding and in pain, Arcos made his getaway from Moncada in the same car as Castro. The two men, both 26 at the time, had been friends for several years from their days in the Orthodox Party, which opposed Batista.

Both were captured, both tried, both convicted -- although Arcos's trial and conviction took place in a hospital, where he was recovering from his wounds. Two years later, as public sentiment for Castro and his valiant revolutionaries grew, the government pardoned all those who survived the Moncada attack. A short while later, Castro went to Mexico to plan his war against Batista. Arcos followed him.

He was typical of many in the group of young revolutionaries Castro gathered around him in the early days of the insurrection. The third of nine children of the administrator of the local waterworks in Las Villas province, east of Havana, Arcos, like most of the rebels, was university educated and middle class. In addition to Gustavo, two more of the Arcos brothers joined the revolution in its early days: Luis, who accompanied Castro on the Granma yacht from Mexico in 1956 and died soon after it landed in Cuba, and Sebastian, who was jailed by Batista for revolutionary activity and freed only after Castro's triumph. Today, Sebastian is a member of Gustavo's dissident human rights group.

When the revolution finally triumphed on Jan. 1, 1959, Arcos, still in Mexico raising money and arms for Castro's army, was jubilant. With a group of Cubans, he stormed the Cuban Embassy in Mexico City, which had been deserted by Batista's diplomats. "Everyone felt as if democracy had won," he says. "You can't imagine a satisfaction and happiness so great. We felt sure there'd be a fairer and more honorable government than the old one. ...

"To me," he adds a moment later, "the Communists were a little party with a few intellectuals and some workers, but a little group compared to those that made the revolution."

Arcos's break with Castro would come later, a free fall from official grace that would cost him two terms -- a total of 10 years -- in prison.

A visitor interrupts the familiar historical account, hoping to steer Arcos back to the present with a question about contemporary Cuba.

Offering a little apology, Arcos explains, "I like to recount these details because it's incredible how public opinion has been manipulated by the revolution to show a different reality."

The reality in Cuba today is that Arcos is one of a tiny and diminishing band of citizens who have undertaken human rights work on an island where such activity is officially considered hostile and may soon be legally designated as treasonous.

Following a brief and unprecedented flowering of the fledgling Cuban human rights movement that was tolerated by the authorities during 1987 and 1988, Castro in the past year has stifled internal dissent. The movement, which never consisted of more than a handful of closely watched, frequently harassed groups, has been all but crushed and all but a few of its leaders imprisoned or exiled.

The group that Arcos helps lead, the Cuban Committee for Human Rights, has just a few dozen members. He joined upon his release from prison in 1988, at about the same time such groups had been given a modicum of breathing room. Since then, the group has applied three times to the Cuban Justice Ministry for official recognition. The applications have been ignored.

Arcos, who was imprisoned from 1981 to 1988 for trying to leave the island illegally, has no salaried job. He receives threats, some veiled, some overt, and frequent warnings that he may be arrested again at any moment for anti-revolutionary activity or illegal associations or some other charge that Castro's regime uses to outlaw and prosecute those who suggest that the revolution tramples on human rights. He and his cohorts are accused of being agents of imperialism and spies for the Yankees.

In fact, Arcos and other Cuban human rights workers have been frequent visitors to the U.S. Interest Section in Havana as well as to foreign embassies, where they keep diplomats abreast of their work and deliver allegations of human rights abuse.

Arcos and most foreign diplomats scoff at the idea that such activity makes him a spy. The Soviet ambassador in Havana, when asked about Cuba's human rights situation, says delicately that different countries are at different phases of maturity when it comes to human rights.

"We've been told that on Saturday, the 'internal enemies' will be severely dealt with," Arcos says. He is speaking on a Friday. Outside is the din of a crashing afternoon downpour. "They try to destabilize us psychologically. They call us and threaten our families. They tell us we've got two choices: Shut up or leave the country."

But Arcos shows no disposition to shut up. And after years of trying unsuccessfully to leave the country, he has now decided that he would rather stay to witness the change he now regards as inevitable.

Like most analysts of events on the island, Arcos is not predicting that Castro's fall is imminent. But in the harsher economic conditions and severe official warnings to dissidents, he sees the desperation of an aging autocrat.

"One of the only arguments that Castro has is that you can't compare Cuba to Eastern Europe," he says. "Sure, no two stones are the same. But they are similar. And people in similar circumstances act similarly. And the idea of democracy that now seems dead in Cuba will rise again."

Not coincidentally, many Cuba-watchers think, the crackdown on human rights activity has intensified as Castro's former socialist allies and underwriters in Eastern Europe have folded one by one. In the face of wishful predictions from Cuban exiles that Castro will soon follow in the footsteps of East Germany's Erich Honecker or Romania's Nicolae Ceausescu, Cuba's leader of 31 years has tightened his already substantial control of nearly every aspect of Cuban life. And he is warning Cubans to expect a draconian austerity program occasioned by dwindling aid from the Soviet Union and the East Bloc.

There have been predictions from academic specialists and some diplomats that the only way Castro could survive the coming trouble would be to provide a safety valve -- to ease up on civil liberties as the economic crunch hits home.

That may yet happen. So far, though, there is no sign of it. Indeed, the opposite appears to be the case: As supermarket stocks dwindle and bus service worsens, Big Brother seems to be watching more closely than ever.

The most visible, or audible, part of the crackdown is that Arcos and the other human rights workers are being subjected to the full rhetorical onslaught of a totalitarian regime.

"Normally they call us worms," Arcos says, a rare, thin smile playing at the corners of his mouth and crinkling his eyes. "We took a step up the ecological scale recently when they called us cockroaches."

Cockroaches with "hairy ears," to be specific.

In 1959, the year of the revolution's triumph, Castro rewarded his loyal aide Gustavo Arcos by appointing him ambassador to Belgium. Based in Brussels, Arcos was also accredited to a handful of Western European countries. He was 32 years old, a young envoy for an infant revolution that had shaken the world at the height of the Cold War.

For Arcos, who had had little exposure outside Latin America, it was a formative experience -- "the happiest, most important, most exciting time of my life," he says.

He traveled widely in Europe, crisscrossing countries on both sides of the Iron Curtain. The contrasts were sharp, and reaffirmed the democratic convictions he thought the Cuban revolution had championed.

"I was comparing the Stalinist regimes I visited with the Western democracies I saw," he says. In the East Bloc countries, "you couldn't talk to anyone about politics because they'd clam up and become afraid. ... People acted passively, mechanistically. Everything was controlled, they were saturated with the official political line. ... You had to wear a mask in public to hide your true feelings."

The news he heard from Cuba at the time surprised him. Priests had been expelled and were losing influence. Arcos, a practicing Roman Catholic who still attends church regularly, got the impression from Cuban students he spoke with in Europe that morality on the island was in decline. Castro had declared himself a Marxist-Leninist, surprising many of his revolutionary compatriots. And there was talk that his cult of personality was spreading.

It started to dawn on Arcos that Castro was creating a communist state patterned in many ways after the East Bloc countries whose problems he had seen firsthand. His disillusionment was crystallized during a visit home in 1965, when he attended the annual May Day parade. Amid the chanting and the choreographed idolatry devoted to Castro, Arcos began to detect the choking sensation of absolute, one-man rule.

"He had created a cult of personality ... the same caudillismo" -- cult of the strong man -- "that Latin America had suffered for centuries and which had always ended up with civil war and death."

He skipped the obligatory protocol visit all ambassadors were expected to pay to Castro. With friends, he began grousing about what had become of the revolution, his dismay at Castro's monolithic grip on Cuban society.

On the ides of March 1966, Arcos, still officially the Cuban ambassador to Belgium, was arrested. He was accused of "discrepancies," by which the regime meant criticism of Castro and of his Marxist ideology.

After three years in prison, he finally was tried on charges of an "improper attitude toward the revolution." Everyone in the courtroom wore the military's olive green, Arcos remembers. The prosecutor declared that his criticism had defamed the revolution and set a bad example for children. It was, Arcos says bitterly, a "judicial farce."

As recognition for his role in the revolution, however, prosecutors did not ask that Arcos be condemned to more time in prison. Instead, they offered him the chance to admit his errors in public.

"I admitted nothing ... it was a problem of dignity and conscience. When I started to speak and the judge realized what I was saying, it was just like in the movies: He banged his gavel and said to the guards, 'Take him away!' "

He was sentenced to 10 more years in prison.

The following year, 1970, he went on a a hunger strike to demand his liberty. After 19 days, the government relented. There was no exoneration -- he was simply let out of prison and told he would have to support himself (effectively denying him employment in a country where most work is for the state).

A short time later he applied to leave the country and was refused. Throughout the 1970s he dreamed of fleeing the island. By 1981, he was desperate. The oldest of his two sons, Gustavo Jr., had been in a motorcycle accident in Miami; his condition was grave.

With his brother Sebastian and his sister-in-law, nephew and niece, Arcos conspired to leave the island illegally. But the very people he thought were helping him turned out to be security agents, and he was arrested on his way to what he thought was a waiting boat. The three men received prison sentences, the two women were freed. Gustavo Arcos got the longest term, seven years, and this time he served the sentence in full. He was released in 1988.

"In Eastern Europe, we've seen that after 40 years, the ideas and organizations of communism have been replaced by pluralism," Arcos says, as if repeating a mantra. "It will be the same here. Here, people are apparently communists, apparently Marxist-Leninists, but most assume that ideological pose as a matter of survival, a modus vivendi."

The authorities, he says, "know that a great part of the country is faking it. ... Appearances deceive -- that's the lesson from Eastern Europe." For that reason, he adds, Castro "is never going to permit a clean game, he'll never permit elections."

Castro himself scoffs at the need for elections, declaring that if he were to propose them the people would think him "mad." Officially, presidential elections are dismissed as patently unnecessary because of Castro's presumed enormous, self-evident popularity.

Not only is Castro unlikely to permit free elections, many Cuba-watchers assert, but the government's campaign of intimidation also makes it virtually unimaginable that Arcos or any of the half-dozen or so men and women who lead the human rights movement could emerge as a Cuban Lech Walesa or Vaclav Havel to challenge him.

Arcos himself makes no claims to national leadership and acknowledges that the membership rolls of Cuba's human rights groups are skimpy dozens, or hundreds at the most. Still, he says, "we're like an iceberg, with only one-sixtieth of our mass showing above the surface."

While he spent most of the 1970s trying to leave the island, today he has decided he wants to remain in the country for a period that he refers to as Cuba's "transition toward democracy."

"What happened in Nicaragua helps us, it gives us enthusiasm," he says. "In the current situation, in this craziness, this crisis, we've decided to stay. We could be useful." If democracy ever comes to Cuba, he says, his group will not seek power, but instead will naturally assume a position of moral authority.

That assertion is a possible explanation for the criticism Arcos has received from hard-line Cuban exiles. In Miami, the rightist Cuban American National Foundation has been busy drawing up blueprints for how it will restructure and revive Cuba after Castro falls. The plan assumes a triumphant return of exiles who will take over the government and introduce democracy; it does not envision a local leader wielding moral authority, a` la Havel.

"He is a threat to those {exiles} who would like to go back to Cuba with the Marines," says Arcos's cousin Arturo Villar, publisher of the Miami-based Spanish-language weekly Vista. "He thinks of himself only as having a moral role more than a traditional political role. But I would suspect that the president of Czechoslovakia would think of himself the same way. I see him in that role, like Havel."

For the moment, if Arcos represents any kind of threat to anyone, it is only in the most abstract sense. Still denied employment, he lives with his second wife, Teresita de la Paz. Married soon after Arcos was released from prison in 1988, they live modestly in rooms nearly devoid of material comfort, supported mostly by the generosity of friends, many of them in exile in Miami.

His oldest son, Gustavo Jr., never fully recovered from his 1980 motorcycle accident. Following exploratory surgery in Cuba last year, he died at the age of 29. Arcos's only surviving child, David, by a first marriage that ended in divorce, lives in the United States. David Arcos, 26, and his father are estranged.

Arcos's time is spent gathering information on cases of alleged human rights abuse, issuing statements and denunciations to the press, diplomats and international human rights organizations. His other task is to inculcate Cubans with a sense of what human rights are -- but without access to media or resources. "It's like an ant's work," he says. "Slow and quiet."

He shuns predictions of when and how democracy will come to Cuba, refusing even to permit himself the luxury of dreaming that he will see it in his lifetime. But he wonders only about how and when -- not whether.

"We're confident that the future will be what we've fought for -- a democratic regime," he says. "Everything here is old and aging, including him {Castro} and his ideas. It's like the old proverb: 'Tomorrow doesn't belong to anyone.'

"We're not prophets, we don't know how it's going to unfold. But you know it's as inevitable as spring following winter. ... And we know when this regime disappears that many sectors who will push for democracy will be those who today are supporting Fidel Castro. That's going to happen."

He smiles at the irony and inevitability of it, a delicious dreamy smile of utter certainty.