NAUDERO, Pakistan - Benazir Bhutto's 19-year-old son was chosen Sunday to succeed her as chairman of her opposition party, extending Pakistan's most famous political dynasty but leaving the real power to her husband, who will serve as co-chairman.

Both major opposition parties also decided to run in upcoming elections, apparently ending the threat of a wholesale boycott as Pakistan struggles to move to full democracy after years of military rule.

Earlier, a spokesman for the country's ruling party said the Jan. 8 vote may be delayed up to four months, saying the parliamentary elections would lose credibility if held as scheduled. He expected a formal announcement within 24 hours.

"How long the postponement will be for will up to the Election Commission," he told The Associated Press. "I think we are looking at a delay of a few weeks ... of up to three or four months."

Bhutto's Pakistan Peoples Party central executive committee met privately to choose her successor three days after the two-time prime minister was assassinated in a suicide attack that thrust the volatile Islamic nation deeper into crisis.

Her son, Bilawal Zardari, a student with no experience in politics, said he would remain at Oxford University, leaving his father, Asif Ali Zardari, who was officially designated co-chairman, as the effective leader of the country's largest political party.

"The party's long struggle for democracy will continue with renewed vigor," Bilawal told a news conference. "My mother always said democracy is the best revenge."

Supporters chanted, "Benazir, princess of heaven" and "Bilawal, move ahead. We are with you."

Bilawal said that Zardari would "take care" of the party while he continued his studies. Zardari then told reporters to direct questions at him, saying his son was at a "tender age."

Zardari, who spent eight years under detention on corruption charges in Pakistan before his release in late 2004, is a party powerbroker who served as environment minister in Bhutto's second government. He has denied the charges of large-scale graft during his wife's rule.

He immediately announced the group's participation in the elections but said that another party leader, Makhdoom Amin Fahim, would likely be their candidate for prime minister if they won.

Zardari appealed to the party of former Prime Minister Nawaz Sharif to drop plans to boycott the polls — planned for Jan. 8 but anticipated by many to be delayed following the assassination.

Sadiq ul-Farooq, a senior member of Sharif's Pakistan Muslim League-N party said it had now agreed to run. "Since the Pakistan People's Party has taken this decision, we will also contest," he said.

The government has blamed an al-Qaida-linked militant for the murder of Bhutto but her party disputes that and claims elements in the Pakistan Muslim League-Q — the ruling party that supports President Pervez Musharraf — could have been behind the slaying.

Zardari repeatedly called the ruling party the "killer league."

He also rejected as "lies" the government's account of how his wife died, amid a dispute over whether she was shot to death or killed by the force of the suicide blast that struck her vehicle as she left a campaign rally on Thursday.

Zardari appealed to the United Nations and British government to help investigate the crime. He said the party wanted a U.N. investigation like the one probing the 2005 assassination of former Lebanese Prime Minister Rafik Hariri.

Zardari also urged supporters who have rioted across Pakistan since Bhutto was slain to show restraint. The violence has left more than 40 people dead.

"We will avenge the murder of Bhutto through the democratic process after winning the elections," he said.

"God willing, when it is the Peoples Party's reign, when the Peoples Party government is formed, then we would have taken revenge for Bibi's blood and that blood would not have gone waste," Zardari said, referring to his late wife by her nickname.