(Agencies)
Updated: 2007-12-02 20:32

CARACAS, Venezuela - President Hugo Chavez would consolidate power and no longer face term limits if Venezuelans approve sweeping constitutional changes Sunday in a contentious vote that has riven South America's top oil exporter.

An emboldened opposition and recent violent clashes involving protesters have raised fears that anger could spill into the streets if the vote is close, as some pollsters predict.

Chavez has warned opponents he will not tolerate attempts to stir up violence, and threatened to cut off oil exports to the U.S. if Washington interferes. His country is a major supplier to the United States, which in turn is the No. 1 buyer of Venezuelan oil.

"In the case of an aggression by the United States government, we wouldn't send any more oil to that country," Chavez told reporters Saturday. "Forget about our oil."

Chavez, who has become Latin America's most outspoken antagonist of Washington since he was first elected in 1998, calls the constitutional overhaul vital. He labels those who resist it pawns of President Bush.

"Anyone who votes 'No' is voting for George W. Bush," Chavez shouted to a sea of supporters Friday. "We're going to give another knockout to Bush."

While the Venezuelan government touts polls showing Chavez ahead, other surveys cited by the opposition indicate strong resistance — which would be a change for a leader who easily won re-election last year with 63 percent of the vote.

Pollster Luis Vicente Leon said tracking polls by his firm Datanalisis in the past week show the vote is too close to predict. Which side wins will depend largely on turnout among Chavez's supporters and opponents, he said.

"If he wins by a very small margin, that's a scenario filled with conflict," Leon said. "In a country where there are high levels of mistrust between the camps, it's obvious the opposition ... would think it was fraud."

In Washington, State Department spokesman Sean McCormack said the United States hopes the referendum will be "a free and fair contest."

Speaking to reporters Saturday, Chavez accused the U.S. government of plotting to discredit what he says will be a legitimate victory for him at the polls.

"They are preparing to disavow the results, so we hope the popular will is respected, whatever it is," Chavez said. "The government of the United States is a threat."

Chavez thanked his ally Nicaraguan President Daniel Ortega for recently "alerting the world to the plan Bush's government has to kill the president of Venezuela." He didn't offer specifics but warned that any assassination attempt would lead to "events that aren't very good for the United States or for the world."