Cuban President Fidel Castro's decision to arrest and try nearly 80 human rights activists, independent journalists and other dissidents is being condemned by governments and activists around the world as a chilling spree of political repression.

Two leading Cuban dissidents who remain free said in telephone interviews Friday from Havana that they had not seen such a widespread crackdown by Castro since the 1960s.

"This is a war against peace and against pacifists," said Oswaldo Paya, the leader of the Varela Project, which has gathered more than 20,000 signatures on petitions that seek a referendum calling for free elections and other democratic openings in Cuba.

"This wave of repression is the worst in the history of Cuba, including during the colonial era," said Elizardo Sanchez, another dissident leader. "Never before have so many people been so severely punished for crimes of thought. They are truly prisoners of conscience."

Human rights activists said Castro was using the Iraq war as a smoke screen to conduct a crackdown and sham trials that Paya said reminded him of tactics used by the Gestapo and the KGB.

"The Cuban government is putting on an extremely ugly show," said Jose Miguel Vivanco, an official with Human Rights Watch in New York.

Cuban officials have called the dissidents traitors who have conspired with the United States to subvert Castro's government. They have said the dissidents can be tried under a law that prohibits assisting the long-standing U.S. economic embargo. But the government has said little else about the trials or the specific charges against the defendants.

Trials continued today for the dissidents, at least a dozen of whom face life in prison. The proceedings, in a Havana courtroom ringed by security forces and closed to international diplomats and foreign journalists, have been criticized by the State Department as "kangaroo courts" and part of the "most despicable act of political repression in the Americas in a decade."

Human Rights Watch, the Committee to Protect Journalists, the Roman Catholic Church and lawmakers and intellectuals from Latin America and Europe have condemned the crackdown. A group of U.S. senators who favor normalized relations with Cuba also sent a letter of protest. Citing deteriorating U.S.-Cuban relations, the Cuban government canceled a major conference on immigration that was expected to draw hundreds of Cuban emigrants to Havana next week.

Castro's crackdown has taken many analysts by surprise because he has been largely tolerant of the growing number of dissidents in Cuba.

Earlier this year, the Cuban government granted Paya unprecedented permission to travel to Europe, where he met Pope John Paul II and received a major human rights award from the European Union, and to the United States, where he met with Secretary of State Colin L. Powell.

It is unclear why Castro has decided to change his tactics.

Sanchez and Paya said the shift started late last year, when police began arresting people in what the government described as a crackdown on drug dealing. The dissident leaders said Castro's forces also quietly arrested scores of people who were challenging the government's control. Most of them were illegally running small businesses and selling food or other goods, a means of survival that the government has tolerated for years in Cuba's dismal economic climate.

Then when the Iraq crisis started heating up, the summary arrests of dissidents began -- Paya said 42 of those arrested are his collaborators in the Varela Project. Several analysts said Castro calculated that the United States was too concerned with Iraqi President Saddam Hussein to worry about Cuba. Or, they said, Castro might have been spooked by the U.S. launch of a preemptive war in Iraq.

"The U.S. is riding high. It thinks it can dictate to or run over anyone and ignore international law," said Wayne Smith, a former top U.S. diplomat in Cuba who is now at the Center for International Policy in Washington. "I'm sure the United States has no intention of having a go at Cuba. But I'm not sure the Cubans are convinced of that."

Smith also said that Castro may be trying to tighten his control ahead of worsening economic times, which have historically led to unrest and attempts to flee the island. Cuba's sugar industry is barely surviving, and tourism is expected to drop significantly as the war continues. "There's a greater sense of uncertainty: Where is the money coming from?" Smith said. "So they are cracking down."

The sense of chaos has been heightened by the armed hijackings of two airliners and a ferry since mid-March. In the most recent incident, Cuban officials on Friday arrested several men who had hijacked a ferry with 50 passengers aboard and tried to make it to Key West before running out of fuel.

Sanchez said the hijackings were "an expression of the discontent and desperation of the people of Cuba -- economic conditions are getting worse every day."

The Cuban government has charged the dissidents with conspiring with the United States, citing their frequent meetings with James Cason, the top U.S. diplomat in Havana. Castro charges that the dissidents are funded by the U.S. government, which the State Department and the dissidents deny.

Paya and Sanchez said Castro is worried that the dissident community has grown from a few people to thousands willing to sign pro-democracy petitions. "Nothing they have done has been enough to paralyze this movement, and that's why they are scared," Paya said.

Paya said he has gone daily to the courtroom where the trials are being held, but security forces have shouted obscenities at him and forced him to leave. Sanchez said he has tried to send observers to the trials but that security police stopped them before they could get within 100 yards of the building.

The extent of Castro's security network came into view Friday, when two reporters who spent years working alongside the country's best-known independent journalist, Raul Rivero, admitted at his trial that they were actually government agents. And in another trial, the secretary of dissident economist Marta Beatriz Roque also acknowledged spying for Castro.

Sanchez and Paya said they did not know why they had not been arrested.

"I am in the hands of God," said Paya, who has become Cuba's most internationally recognized dissident. "If I am not here tomorrow, we need the solidarity of people all over the world. We don't have oil, but we have 11 million people. We need the hearts and voices of people everywhere demanding freedom for the prisoners and peaceful change in Cuba."

A dissident arrived in a police car at Havana's High Court of Justice in March. At least a dozen dissidents are facing sentences of life in prison. Blanca Reyes, wife of Raul Rivero, talks on the phone as she sits with Alida Viso, wife of Ricardo Gonzalez. Journalists Rivero and Gonzalez are among nearly 80 people facing trial.