BOGOTÁ, Colombia (By Juan Forero, NYTimes) November 30, 2005 — Accusing Venezuelan electoral officials of favoring that country's populist government, three opposition parties announced Tuesday that they would pull out of congressional elections scheduled for Sunday.

The withdrawal of the three parties, two of which governed Venezuela for four decades until President Hugo Chávez won office in 1998, could give the leftist governing party overwhelming control of the 167-member National Assembly. If Mr. Chávez's slim majority in the Assembly increases to a two-thirds majority, the government will be poised to obtain a range of constitutional reforms, like an extension of the president's term.

"Under these conditions, we cannot participate in the electoral process," Henry Ramos, the secretary general of Democratic Action, told reporters on Tuesday.

Democratic Action and officials of two other parties, the Social Christian Party, or Copei, and the smaller Project Venezuela, accused the electoral authorities of failing to correct errors in the voter registry and in electronic voting equipment, opening the door to fraud and discrimination against opponents of the government.

"Across this country, there is a profound lack of confidence in the electoral arbiter because it does not say the truth," said César Pérez Vivas, secretary general of Copei, which had asked that the elections be delayed.

Mr. Chávez, though, called the opposition pullout "political sabotage" and said it would not discredit his government. Other officials said the vote would take place as planned and harshly accused the opposition of withdrawing because it faced a dire outcome at the voting booth.

"Very well, let them go to hell," Vice President José Vicente Rangel, told reporters. "They know they are defeated because they see the polls, too."

Mr. Rangel and allies of the president also accused the United States of playing a role in the collective withdrawal of the parties, noting that an election-monitoring group that receives financing from Washington, Súmate, called for Venezuelans to gather in churches on Sunday and raise their voices in anti-government prayer.

The three parties that are withdrawing hold 36 seats in the Assembly. Three other important opposition parties will take part in the election, but the absence of Democratic Action and Copei is expected to be a blessing for Mr. Chávez's Fifth Republic Movement and its allies, which control nearly 90 seats.

"It's a disaster, a disaster for the opposition," Luis Vicente León, a political analysts who heads the Datanalisis polling company, said by phone from Caracas. "Only a small part of the opposition will participate, and that's a disaster."

Mr. León said the withdrawal of the parties would give Mr. Chávez and his allies more than 80 percent of the National Assembly, 10 percent more than they would have won had the opposition parties not withdrawn.

Since their resounding defeat in a recall referendum against Mr. Chávez last year, an opposition umbrella group has disappeared and many of its leaders have fallen into obscurity. Last year, the government swept regional elections, leaving the opposition in control of only two of 23 states.

Mr. Chávez, meanwhile, has until recently held a popularity rating approaching 70 percent as his government spends generously on social programs for the poor. The president is expected to be easily re-elected to another six-year term next year.