CARACAS, Venezuela (AP) _ Opponents of Venezuelan President Hugo Chavez are demanding further investigation of what they call gross irregularities in the voter registry, pointing to a western state where 1,921 people by the name of Gonzalez are listed with an identical birthday.

The electoral council, which is independent but faces accusations that it is pro-government, insists the lists are sound, and plans to release an external audit Tuesday as it prepares for December presidential elections.

The case of the many Gonzalezes in Zulia state was reported by Roberto Ansuini, an opposition-aligned researcher and former member of the National Electoral Council who analyzed a database of more than 2 million new voters registered since 2003.

The first names ranged from Armando to Victor, but all 1,921 Gonzalezes turned 32 on March 15 and all were from Zulia, according to the list compiled by Ansuini, a member of the Social Christian Party, which boycotted congressional elections last year citing concerns about the voting system.

``It's statistically impossible,'' Ansuini said.

Although the name Gonzalez is ubiquitous in Venezuela, Ansuini said citizenship records show that no more than 89 Gonzalezes have been born on any other day in Venezuela's history. The discrepancy, he said, suggests manipulation.

But the president of the electoral council, Jorge Rodriguez, said last month that an investigation found that only 61 of the 1,921 Gonzalezes were wrongly listed.

``The rest had a perfect right'' to vote as listed, he said.

Besides, he said, 1,921 people are a tiny fraction of Venezuela's 14.8 million voters.

Rodriguez said the electoral council also sought an audit from the Costa Rica-based Electoral Consulting and Promotion Center of the Inter-American Institute of Human Rights. The center has presented its report to electoral officials, who plan to release findings Tuesday.

Ansuini and other Chavez critics questioned the audit's independence and accused the electoral council of siding with Chavez _ an accusation Rodriguez strongly denied.

The leftist president has accused opponents of making up false claims, and he says U.S. President George W. Bush's government is quietly backing an effort to discredit a sound electoral system. Chavez harshly insulted Bush on Sunday, calling him a ``donkey'' and a ``drunkard'' days after Bush labeled him a demagogue.

``He's the boss of the Venezuelan opposition,'' Chavez said.

He has pointed to U.S. funding for groups like Sumate, which took money from the U.S.-based National Endowment for Democracy, a group funded by the U.S. Congress. Sumate and the NED insist they have done nothing wrong.

Sumate claims there are some 28,000 voters listed with pre-1900 birth dates, and are demanding that the voter registry be published each month with voters' addresses _ now kept confidential for privacy.

International observers have largely backed Venezuela's recent election results, including a 2004 recall referendum easily won by Chavez.