CARACAS, Venezuela, Aug. 18 - After demanding an audit of voting results upon failing to oust President Hugo Chávez in a recall referendum, representatives of Venezuela's opposition movement said Wednesday that they would refuse to participate in or recognize the review, asserting that the audit would fail to detect the deception that they insist took place.

The opposition has not offered solid evidence of wrongdoing to the Organization of American States or to the Carter Center, monitors of the 18-hour recall election on Sunday in which a large margin of Venezuelans voted to keep Mr. Chávez as their leader.

Both organizations said that their so-called quick count sampling of voting results on Sunday showed that Mr. Chávez had easily won.

But on Tuesday, Jimmy Carter, the former American president and leader of the Carter Center, which is based in Atlanta, said both monitors would oversee an audit of 150 voting tables - each with two or three voting machines - to dispel accusations of vote tampering.

On Wednesday, though, leaders of the anti-Chávez movement in Venezuela announced that the audit should not proceed because they had evidence that hundreds of machines had been manipulated to limit yes votes on the recall.

"We have given the order not to participate," Enrique Mendoza, an opposition leader, told reporters. "The results of this audit cannot be considered valid to satisfy the opposition's demands."

An official with the Organization of American States, however, said the monitor group had rejected the opposition's demand that voting machines be reviewed and tested.

Instead, the audit would go ahead on Thursday as planned, with the results ready in two or three days. Paper ballot receipts from across the nation would be compared in Caracas with the electronic results from the new voting machines, which were operated by Smartmatic, a company based in Boca Raton, Fla.

Officials of both the Carter Center and the Organization of American States said the audit was an infallible method of detecting irregularities. They also said that the voting machines had worked flawlessly on Sunday and that there was no evidence of tampering.

The opposition took part in a smoothly conducted pre-election audit of a sampling of voter machines, after tamper-proof software was installed that allowed the machines to record votes and transmit results to a central vote-counting bank.

"The system is designed to allow maximum transparency and security, and we welcome additional audits to demonstrate accuracy," Mitch Stoller, a spokesman for Smartmatic, said.

The opposition's insistence that the government had cheated, despite the assurances of monitoring officials, prompted a harsh rebuke from the Venezuelan authorities.

"They know that with the audit they will still look ridiculous before this country," said Mari Pili Hernández, a government spokeswoman. "Why? Because they have no evidence."

The opposition's claims are based largely on surveys of voters by members of Súmate, an antigovernment group that received $53,000 from the National Endowment for Democracy, a United States government organization whose stated mission is to promote democracy around the world.

Sumate also conducted a quick count sampling of votes similar to that conducted by the Carter Center and the O.A.S. that also showed the government had won. But opposition leaders seized instead on the surveys to support their case.

Mr. Carter has dismissed such voter surveys as inaccurate and has said that the quick count, which has a margin of error of plus or minus one percentage point and is used in elections worldwide, is a much more accurate measure.