HAVANA -- With a flourish and a mighty stroke of the pen, President Fidel Castro on Saturday launched his latest defensive move against capitalism, a "populist referendum" to enshrine socialism in Cuba's constitution.

In a televised ceremony following an address in the town of Cacahual, outside Havana, to a crowd of 50,000 celebrating the birthday of revolutionary icon Ernesto "Che" Guevara, Castro put his name to a copy of the Constitutional Amendment he says was the project of mass organizations, not his government.

But members of the country's illegal but tolerated dissident groups said the "referendum" -- which allows only a "Yes" vote or an abstention -- was a transparent ploy to foil Cuban aspirations to democracy, AFP reported.

"This shows the fundamentalism of the government," said high-profile dissident Elizardo Sanchez Santa Cruz of the opposition Cuban Human Rights Commission.

"They are trying to head off the Varela Project," he said, refering to a petition bearing more than 11,000 signatures seeking a referendum on political pluralism and market-minded economic change.

It was not until former U.S. President Jimmy Carter made his historic trip to the tiny island in May and spoke publicly of the dissident effort that many Cubans even learned of the Varela Project.

Some 130,000 "polling stations" opened around the country early Saturday and were expected to remain open until Tuesday for Cuba's 11 million people to sign on to the latest manifestation of the 43-year-old revolution.

"We will show our steadfast fidelity to the country, to the revolution and to socialism," Castro told the crowd at Cacahual, the latest gathering in a week of mega-demonstrations around the island in protest of U.S. foreign policy and U.S. accusations that Cuba was developing biological weapons.

"Imperialist domination and the capitalist system will never come back to Cuba," Castro said. "All of these demonstrations have no other goal than to respond to (U.S. President George W.) Bush," who, in recent weeks, has affirmed his continued support of the four-decades-old U.S. economic embargo until democracy reigns on its tiny Caribbean neighbor.

Castro also blasted U.S. officials who accused Cuba of manufacturing biological weapons, describing them as "crazy," "idiots" and "liars." From Washington, State Department Spokesman Philip Reeker on Friday told reporters that rather than addressing the Varela Project, "Castro has chosen to manufacture an alternative petition supporting the current Constitution and to intimidate the population into signing it." "Obviously, given Castro's control over the Cuban population, he is no doubt going to try to get more signatures on this than on Project Varela and make arguments to that effect," Reeker said.

For some, like 67-year-old Etelvina Gomez, the choice to sign was easy.

"I come to support Fidel and to support my homeland," said the resident of Vedado, a neighborhood in central Havana, who was welcomed to the polling place by a group of Communist Party supporters dressed in red T-shirts emblazoned with the face of Che.

"I am going to sign because I don't want to have problems at work," said a Havana hotel receptionist who chose not to give her name.

"The policy does not interest me; I just want to live peacefully." Sergio Ruetalo, an electrician, said he would sign because he did not want to compromise his family -- including a sister enrolled in university. And anyway, he said, "If it opposes the Americans, I will sign."