Updated

President Hugo Chavez urged supporters to approve constitutional changes that he said could keep him in power for life and threatened to cut off oil exports to the United States if it tries to meddle in Sunday's vote.

Speaking to more than 200,000 supporters on Friday, Chavez warned that his opponents at home could try to sabotage the vote with backing from Washington through violent protests on the night of the vote.

"If 'yes' wins on Sunday and the Venezuelan oligarchy, the violent Venezuelans — the ones who play the (U.S.) empire's game — unleash violence with the tale that there was fraud ... minister, that very Monday you order a halt to the shipments of oil to the United States," Chavez said, addressing his oil minister, Rafael Ramirez.

"Oil will not go out to the United States," Chavez said, warning the opposition if they take to streets to deny a legitimate victory, "they're going to regret it."

Venezuela was the fourth largest oil exporter to the United States in 2006.

Chavez dismissed Venezuelans who oppose the constitutional changes as beholden to U.S. interests.

"Anyone who votes 'No' is voting for George W. Bush," he said. "Our real enemy is called the U.S. empire, and on Sunday, Dec. 2, we're going to give another knockout to Bush, so no one forgets that is the battlefield."

Chavez's opponents have called for close monitoring of results in what they expect to be a tight contest, raising tensions ahead of a vote on sweeping changes that would left Chavez seek re-election in 2012 and indefinitely.

His opponents have called for close monitoring of results in what they expect to be a tight contest, raising tensions ahead of a vote on sweeping changes to the constitution that would left Chavez seek re-election in 2012 and indefinitely.

"If God gives me life and help," Chavez said, "I will be at the head of the government until 2050!" — when he would be 95 years old.

"To the Venezuelan oligarchy and the U.S. empire, from here I'm warning them that they won't be able to stop the car of the Bolivarian Revolution, because on Sunday we will approve the constitutional reform," Chavez said.

There were no independent crowd estimates, but reporters estimated the crowd at more than 200,000.

The government cites polls showing Chavez leading ahead of the referendum, while other polls have predicted a close race.

Pollster Luis Vicente Leon, whose firm Datanalisis found the "no" option leading in a poll earlier this month, said Friday that two other later tracking polls by his firm found Chavez had closed the gap and the two sides were statistically about even.

"We don't know who's going to win," Leon said. "The result will depend on the level of abstention that ends up happening. Whoever has the greatest weight to achieve turnout among their voters at the polls is going to win."

In Washington, State Department spokesman Sean McCormack said the United States hopes the referendum will be "a free and fair contest in which the will and desire of the Venezuelan people is reflected."

Speaking to the crowd from a stage, Chavez said: "Venezuela is going to be a world power, no matter whom it hurts!"

The pro-Chavez rally came a day after opposition supporters filled the same avenue promising to defeat revisions that would also extend presidential terms from six to seven years, create new forms of communal property and expand Chavez's powers to reshape Venezuela as a socialist state.

"Chavez has become a father for us," said Xiomi Diaz, a 34-year-old farmer. "He's a father of the poor." She and others traveled from across the country in hundreds of buses, and chanted: "Ooh, Ah! Chavez isn't going anywhere!"

Chavez, who was first elected in 1998, denies he is trying to amass power, saying the changes are necessary to give the people a greater voice in government and to move toward a socialist system.

Human Rights Watch warned the reforms would threaten fundamental rights, citing one revision allowing the president to declare indefinite states of emergency during which the government could detain citizens without charge and censor the media.

"These amendments would enable President Chavez to suspend basic rights indefinitely by maintaining a perpetual state of emergency," said Jose Miguel Vivanco of the New York-based group.

Chavez's opponents also have questioned the National Electoral Council's impartiality, especially after Chavez named its former chief, Jorge Rodriguez, as his vice president in January. But in contrast to past elections, when the opposition has boycotted votes or been split on whether to participate, this time many opposition leaders are emboldened and urging voters to turn out in large numbers.

University students have led protests and occasionally clashed with police and Chavista groups. One man was shot dead Monday while trying to get through a road blocked by protesters.

The opposition also has been heartened by some recent defections from Chavez's movement, including former Defense Minister Gen. Raul Baduel. Even Chavez's ex-wife, Marisabel Rodriguez, has urged Venezuelans to vote "no."

About 100 electoral observers from 39 countries in Latin America, Europe and the United States are on hand, plus hundreds of Venezuelan observers, the National Electoral Council said.

Yet, absent this time are the Organization of American States and the European Union, which have monitored past votes.

Among those attending are observers from the National Lawyers Guild and the National Association for the Advancement of Colored People.

Chavez's opponents have been suspicious of electronic voting machines made by Boca Raton, Florida-based Smartmatic Inc., which is primarily owned by three Venezuelans. But Luis Enrique Lander of the Venezuelan vote-monitoring group Ojo Electoral said his team is satisfied with vote preparations and safeguards.

Chavez also threatened to expel journalists for the CNN international news network if they assisted in any plot to overthrow his government.

If CNN "came here to lend its correspondents to an imperialist operation, they will be thrown from the country," Chavez said.

On Tuesday, he accused the network of promoting his assassination, after CNN en Espanol aired a picture of him and his Colombian counterpart Alvaro Uribe with the words "And who killed him?" superimposed.

CNN said the airing, which lasted a few seconds, was a mistake, and the text corresponded to another news item that had nothing to do with the presidents' images.

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