The Cuban dictator, Fidel Castro, in a move seen as a sign of fear and weakness, staged a massive protest in Havana yesterday, denouncing President Bush’s “hypocrisy” on terrorism and calling for the arrest of Cuban exile and Castro opponent Luis Posada Carriles.

Mr. Posada was detained yesterday afternoon in Miami by officials of the Immigration and Customs Enforcement agency, according to a statement issued by the Department of Homeland Security, which oversees the agency.

The demonstration and Mr. Castro’s incitement come days before a major pro-democracy meeting – a gathering of the Assembly to Promote Civil Society in Cuba – planned to open on Friday. The meeting is a nonviolent convention of 365 Cuban groups in Havana to discuss, among other issues, fostering democratic reform in Cuba, reducing poverty, securing labor rights, and protecting the environment.

The Assembly was probably the motivation behind Mr. Castro’s antics, rather than the Bush administration’s position on terrorism or its stance on Mr. Posada, scholars of Cuba said yesterday.

A Cuban-American and former State Department official, Otto Reich, said that it was “standard operating procedure” for Mr. Castro to drum up anti-American sentiment and to try to engage America when confronted with domestic public opposition.

“He cannot allow it. He’s terrified,” Mr. Reich, who also served as America’s ambassador to Venezuela under President Reagan, said.

According to the Associated Press, Mr. Castro turned out hundreds of thousands of protesters in a “March Against Terrorism” past the American Mission in Havana yesterday morning to demand the arrest of Mr. Posada. He is accused of involvement in the 1976 bombing of a Cuban aircraft that killed 73 people. At the march, the AP reported, Cuban children shouted “Bush, terrorist!” and “Punishment for the assassins!”

Mr. Posada had recently surfaced in Miami, granting interviews to Florida members of the city’s press.

During his meeting with South Florida reporters yesterday, Mr. Posada said he would reconsider his petition for asylum in America if his request would prove problematic for the American government. Following that conference, according to reports by the Miami Herald, the exile was detained.

The Associated Press reported yesterday that Cuban officials are asking that Mr. Posada be extradited to Venezuela. A State Department spokesman, Richard Boucher, confirmed yesterday that the department had received a provisional arrest request from the government of Venezuela.

According to the DHS statement, however, America “does not generally remove people to Cuba, nor does ICE generally remove people to countries believed to be acting on Cuba’s behalf.”

To a scholar at the American human rights organization Freedom House, Sandy Acosta, however, the Havana demonstration and the Posada affair amounted to a “diversion,” meant to take the world’s focus away from the Assembly and any related crackdowns on dissidents.

According to reports out of Havana and Miami, the crackdown is under way, and arrests are already being made in connection with the Assembly. The event’s organizers said yesterday that the delegate from the Cuban province of Camaguey, Jose Antonio Mole Porro, was detained on Sunday by Cuban police shortly before his intended departure for Havana. According to the Assembly’s reports, Mr. Mole’s wife said no reason was given for the arrest of her husband, who also runs an independent library on the island – an offense often resulting in imprisonment.

“Obviously, they don’t want the world to focus on the fact that there’s a lively and active dissident movement in Cuba, and mass discontent with the system,” Ms. Acosta, who is part of Freedom House’s Cuba Democracy Project, said.

The director of the Washington based Center for a Free Cuba, Frank Calzon, said that Mr. Castro’s diversion tactic is “a measure of how weak he thinks he is.”

A legitimate and freely elected leader, Mr. Calzon said, doesn’t need to rally hundreds of thousands of people to support of him when confronted with hundreds of nonviolent dissidents. “He feels threatened by this group – and these are folks that don’t have any weapons, they don’t have any access to national media. These are people who just want to meet to discuss Cuba,” Mr. Calzon said.

Mr. Reich, too, said Mr. Castro was staging yesterday’s demonstration out of fear of Friday’s gathering. “He’s terrified that this will snowball into something bigger,” Mr. Reich said.

The former ambassador expressed skepticism, however, that the march and the flap over Mr. Posada would quiet the island’s dissidents. “So I wouldn’t be surprised if he tries something dramatic” later in the week, Mr. Reich said. “He probably has it planned already,” he added.

Mr. Reich and others pointed to Mr. Castro’s recent record of exploiting anti-Americanism to obscure internal repression. In March 2003, the Cuban dictator used the cover of the Iraq war to round up and jail 75 independent librarians, academics, journalists, and other democracy activists in what is known on the island and in the exile community as the “primavera negra,” or “black Spring.”

Just before the last similar attempt to stage a major pro-democracy gathering in Cuba – a planned meeting of a human-rights organization, the Concilio Cubano, in February 1996 – Cuban MIGs downed two civilian aircraft, operated by an American-based Cuba-relief organization, Hermanos al Rescate, over international waters. The action killed three American citizens and an American resident of Cuban origin. The incident, scholars said, was designed to draw attention away from Mr. Castro’s crackdown on organizers of the failed Concilio Cubano meeting.

Given the dictator’s record, Mr. Reich said, Mr. Castro was “capable of anything” this week, including possibly a diversion resulting in loss of life,” and maybe not even involving Cubans alone,” he added, referring to the American deaths in 1996.

That threat and yesterday’s events, however, seem unlikely to deter members of the Assembly.

Reached by phone yesterday at his home in Havana, one of the Assembly’s principal organizers, dissident Rene Gomez Manzano, discounted yesterday’s protests. While the Web site of the official daily publication of the Cuban state, Granma, reported yesterday that 1.2 million Havana residents had taken to the streets at their leader’s urging, Mr. Gomez said, in Spanish, that it is a “mechanism of the totalitarian regime” to send officials to schools and workplaces to force Cubans to participate in such demonstrations.

“A normal person sees this number of people, and says, ‘What support!’ ” Mr. Gomez said. “For someone not from a totalitarian country, it is not easy to understand,” he added.

He estimated that fewer than 5% of yesterday’s protesters had any sort of understanding of or sympathy toward the cause for which they were marching.

Indeed, most Cubans, Mr. Gomez said, “totally reject the government,” even if they remain silent about their views out of fear of the police state. As a result, the gathering of Cubans at the Assembly, he said, was extremely important, as were international expressions of solidarity for those risking their personal safety to openly advocate democracy in Cuba.

The fact that so many Cubans were willing to “put their faces, their names, and their identities” to the cause of the Assembly, Mr. Gomez said, indicated “a tremendous success.”

Despite the arrests and resistance from the regime so far, Mr. Gomez said it appeared the Castro government was more likely than not to permit the Assembly to take place. If the convention is held, he said, Friday will mark “a turning point in the entire trajectory of the dissident movement.”

“In the future, Cuban history will be divided into Before the 20th of May and After the 20th of May,” Mr. Gomez said.