When Cuban president Fidel Castro took power, in 1959, Oswaldo Payá was in primary school — the only kid in the entire school who refused to become a Communist Youth member. In high school, after openly criticizing the 1968 Soviet invasion of Czechoslovakia, Payá was sent to a Cuban labor camp for three years. Rather than escape to Miami in the 1980 Mariel boatlift, he stayed in Cuba to work for democratic reform. More than two decades later, his efforts are suffering a backlash — they moved Castro to launch his harshest crackdown ever. In the past few months, 54 leaders of Payá's dissident groups — the Christian Liberation Movement (MCL) and the Varela Project — have been convicted of treason and sentenced to lengthy prison terms. But Payá, 51, insists his movement is still strong. "We're the first nonviolent force for change this island has ever known," he told Time. "Castro can't crush that, no matter how hard he tries."

Cuba's communist regime has rarely if ever faced a dissident who is as hardheaded as Castro himself. Payá, an engineer and devout Roman Catholic who cycles each day to his job as a hospital-equipment repairman, is right when he calls the MCL Cuba's first real dissident force in 44 years — the first, anyway, to convince tens of thousands of Cubans to forget their fear and sign petitions seeking a referendum on democratic freedoms. That effort won Payá the European Union's Sakharov Prize for human rights last December; but it also moved Castro, 76, to respond with a wave of arrests. Castro has been careful not to jail the internationally popular Payá, who likens his movement to the Prague Spring that preceded the Soviet crackdown of '68. "This is a Cuban Spring," says Payá. "It will lead to the civil rights we're demanding."

Can Payá do in Cuba what Vaclav Havel did in Czechoslovakia? Castro's rule has proved more durable than the Iron Curtain. But Payá is unique, says José Miguel Vivanco of Human Rights Watch in Washington, D.C. Instead of trying to overthrow Castro — as the U.S. has tried to do with its failed 41-year economic embargo — Payá "is openly challenging Castro's system by using the system itself." Payá's Varela Project has collected the signatures needed for a plebiscite — permitted under Castro's constitution — on free speech, multiparty elections and expanded private enterprise.

Castro refuses to recognize the project, but the grass-roots movement it generated probably has him choking on his rum mojitos. Despite Castro's push to develop tourism, Cuba's economy is a shambles, and a hoped-for easing of the U.S. embargo has been quashed by George W. Bush. The last thing Castro can afford now is a Solidarity-style movement. So in March, with the aid of agents who had infiltrated the dissident cells, he rounded up 78 dissidents and independent journalists, including Payá's captains. In his May Day speech last week, Castro branded them "mercenaries on the payroll of Bush's Hitler-like government," which he claims is poised to invade Cuba. To demonstrate his new wrath, Castro's government last month executed three Cuban men who tried to hijack a ferry to Miami.

Many human rights experts fear Castro may now have succeeded in neutralizing Payá. The U.N., which in a stunning display of bad timing re-elected Cuba to its human rights commission last week, has given Castro little more than a slap on the wrist — as have his Latin American neighbors. But Europe's legions of Castro admirers, from politicians to artists, are increasingly siding with Payá, a phenomenon that could dampen European enthusiasm for travel to Cuba, which is often driven by the island's chic revolutionary cachet. Portugal's Nobel-prizewinning novelist, José Saramago, once a Castro admirer, wrote in a stinging editorial last month that "this is as far as I go" with Cuba's revolution. The E.U. has also postponed negotiation of a badly needed economic aid package for Cuba. At the same time, Payá — who like most Cuban dissidents opposes the U.S. embargo because it gives Castro a convenient political scapegoat — has altered the thinking of anti-Castro forces in the U.S. Since many of them see in Payá the first real chance to grow democracy from within the country, even hard-line exile groups like Miami's Cuban American National Foundation are advising Bush not to tighten the embargo. Last week, a bill was reintroduced in the Senate that would abolish the U.S. ban on travel to Cuba.

Wresting the Cuba debate away from the pro- and anti-Castro extremists may be Payá's most significant accomplishment. "This isn't about war mongering anymore," he says. "It's a duel between power and spirit." For now, Castro's power has the upper hand; but for four decades Payá's spirit has been indomitable — and he insists he's not about to give up now.