Venezuela?s opposition leaders said this week that they had given observers evidence of electronic vote tampering that helped President Hugo Chavez win Sunday?s referendum, but they boycotted an audit planned to clear up their fraud charges.

Observers, led by former US President Jimmy Carter and the Organization of American States, say they have seen no evidence of vote manipulation so far. But they have agreed to additional checks on a sample of the results.

Opposition leaders on Wednesday refused to take part in the audit because they said it could not properly investigate the referendum which gave victory to Chavez, a left-wing former army paratrooper first elected in 1998.

They charged at least 500 polling stations out of 12 000 nationwide used voting machines preprogrammed with an artificial cap to limit the number of votes cast in favor of recalling Chavez.

?We are not going to accept the results until all of these doubts have been cleared up,? said opposition leader Enrique Mendoza. ?It doesn?t matter how long it takes, we will keep denouncing this every day.?

The international community had hoped a clear vote on whether Chavez should step down would end the bitter struggle over the populist leader?s presidency, but the fresh dispute could inflame tensions in the world?s No. 5 oil exporter.

National Electoral Council official Jorge Rodriguez on Wednesday rejected the tampering accusations as ?irresponsible? and ?criminal? fabrications. ?The machines were never reprogrammed,? he said.

Even without opposition support, observers yesterday began an audit on 150 polling stations to check electronic vote tallies against printed confirmation ballots. The checks should end at the latest on Friday, officials said.

Firebrand nationalist Chavez has declared his victory a reconfirmation of his ?revolutionary? reforms to improve the lives of the poor. Government officials have also dismissed the fraud charges.

Venezuelans participated in huge numbers ? 10 million of nearly 14 million registered voters went to the polls. The recall effort was led by critics who accuse Chavez of authoritarian rule and manipulating the courts and electoral council in an effort to stay in power.

With 96 percent of the votes counted, 5.55 million or 59 percent of voters cast ballots against Chavez?s recall, while 41 percent or 3.84 million voted to end his mandate, the National Electoral Council said on Wednesday.

The outcome left opposition supporters bitter that they failed to oust Chavez. The president has already survived a brief coup, a grueling oil strike and months of street protests.

Opposition protesters sprayed ?fraud,? ?dirty rats? and ?thieves? on the Caracas office of Smartmatic, the company that made the voting machines. Military police later arrived to guard the building. The country has remained generally calm after the vote.

Observers stood by their earlier support of the results.

?The mission established that the majority of the voters chose not to revoke the mandate of President Hugo Chavez,? the OAS said in a statement.

The United States, a chief customer for Venezuelan oil, has urged authorities to clear up the fraud charges to allow Venezuelans to heal the deep divisions caused by more than two years of confrontation over Chavez?s presidency.

<B>Patrick Markey</B>