Insisting that congressional elections will be conducted fairly, Venezuelan President Hugo Chavez is accusing the opposition of trying to derail the vote by pulling out just days before it's to take place.

Two opposition parties withdrew Tuesday from the elections, saying conditions were biased toward allies of the leftist Chavez. A third party threatened to boycott unless the vote scheduled for Sunday is postponed to ensure fairness.

The Venezuelan leader, who is a vocal critic of President Bush, called the move a last-ditch political stunt pulled by an enfeebled opposition that analysts have predicted would be soundly defeated at the polls.

"What fraud? They should accept the truth that they have no public," he said. "It's an attempt at political sabotage."

The defections boost Chavez's chances of winning the two-thirds congressional majority he needs to push through constitutional reforms. One of those reforms is an amendment that would strike down a limit on presidents to two six-year terms, a period that would expire for Chavez in 2012 if he is re-elected next year.

Currently, pro-Chavez lawmakers hold 52 percent of the 165-seat National Assembly. The defectors -- major opposition party Democratic Action and the smaller Project Venezuela -- together hold 30 seats. The Social Christian Party, or Copei, which has threatened to boycott, holds six.

Chavez, speaking during a ceremony to tout a new train project, said candidates should run to uphold their pledge to the electorate.

"What are they going to tell their people ... after having called elections for months?" Chavez said.

The three parties claim the National Elections Council is biased toward pro-Chavez candidates and allege the candidates used public funds for campaigning. They also opposed the use of high-tech thumbprint identification devices that the council said Monday would not be used.

Democratic Action and Copei long dominated national politics before Chavez's meteoric rise to power in 1998 elections. The centrist parties differ little in ideology and are united in their fierce opposition to Chavez, who says he is leading a socialist revolution to help the poor. This election could mark the first time since Venezuela's last dictatorship fell in 1958 that neither party fields a candidate.

Chavez said the two parties during their half-century of domination "did whatever they wanted, plundered the country and handed it over to imperialism."

He also accused them of receiving U.S. financial backing and of being the same people who backed a short-lived coup against him in 2002.

"Let them leave! We don't need them," he said Tuesday.

Henry Ramos of Democratic Action denied government accusations that the opposition has been acting in the interests of the U.S. government, which is often critical of Chavez. He also took a dig at Chavez for his close ties with Cuban leader Fidel Castro.

"We don't sit on the U.S. ambassador's lap, nor do we sit on the Cuban ambassador's lap," Ramos said.

The parties' influence has been flagging, and recent polls show Chavez has a nearly 70 percent public approval ratings.

Luis Vicente Leon of the Venezuelan polling firm Datanalisis has said that with fewer opposition parties participating, it will be a "disaster for the opposition."

"The loss will be dramatic," he predicted.