ISLAMABAD, Pakistan, Dec. 9 — The two main opposition parties led by Benazir Bhutto and Nawaz Sharif said they would participate in Jan. 8 parliamentary elections, despite deep misgivings about whether the vote could be free and fair.

The move came as an opposition call to boycott the elections foundered Sunday.

Mr. Sharif, the former prime minister who returned from exile two weeks ago but has been barred from running himself, would marshal his party to contest elections, Ahsan Iqbal, a party spokesman said.

Mr. Sharif had called for a boycott of the election to protest the continued rule of Pakistan’s president, Pervez Musharraf, who imposed a state of emergency on Nov. 3, suspending the Constitution and dismissing the Supreme Court. But when Ms. Bhutto, also a former prime minister, made it clear that her party would run, Mr. Sharif could not afford to stay out of the race, Mr. Iqbal said.

The parties that will participate say they are doing so “under protest,” and that they will mount a campaign against unfair election conditions and the government’s efforts to return a Parliament and government favorable to Mr. Musharraf.

The participation of the main opposition parties would grant some credibility to Mr. Musharraf. Opposition groups that support a boycott argue that fair elections would be impossible with the country still under emergency rule, the news media muzzled, and a pro-Musharraf caretaker government, election commission and newly appointed Supreme Court in place.

Ms. Bhutto said her Pakistan Peoples Party would participate in the elections in order to force them open and prevent the pro-Musharraf coalition from winning a majority.

“We believe it is important to take part under protest because by boycotting we play into the hands of Musharraf,” she said in a telephone interview on Sunday from her home in the United Arab Emirates, where she spent the weekend.

Ms. Bhutto has said she fears the government would try to rig the elections by stuffing ballot boxes in the provinces, among other measures.

Mr. Musharraf has said he will lift emergency rule on Dec. 16 and has pledged to hold “fair and free elections according to the Constitution.”

Meanwhile, Mr. Sharif’s marshaling of his supporters represents a strong challenge to Mr. Musharraf. Mr. Sharif leads a faction of the Pakistan Muslim League and his base of support is Punjab, Pakistan’s most populous province and the most important in the electoral college. His participation is likely to cut into the strength of the bloc of the Pakistan Muslim League that supports Mr. Musharraf.

Ms. Bhutto was in talks with opposition parties earlier in the year to mount a united democratic front against Mr. Musharraf, who has ruled Pakistan since seizing power in a coup in 1999. But in recent months, she also opened negotiations with Mr. Musharraf over a power-sharing arrangement that would have allowed her to become prime minister as Mr. Musharraf stepped down as army chief to become a civilian president.

Since her return to Pakistan on Oct. 18 — and in particular after she was placed under house arrest twice and hundreds of workers in her party were arrested — her relations with Mr. Musharraf have deteriorated, prompting her to find common ground with other opposition parties.

Any future cooperation with the general would depend on how the elections proceed, Ms. Bhutto said.

“It is not clear that these elections are going to be fair, it depends on the fairness issue,” she said. “I would like to wait and see if the elections are fair and if Musharraf is an instrument for democracy or if he is an obstacle to a democratic Pakistan.”

Ms. Bhutto said her party had learned that boycotting elections, as it had in 1985, was a mistake because it allowed the military government at the time to handpick the Parliament and government, leaving opposition parties sidelined for five years.

“Our vote bank shrank, some of our leading candidates disappeared and people emerged on the political scene who spent their energy on ethnic, lingual and sectarian differences,” she said.

The opposition parties have been drawing up a list of demands for the government to address to ensure free and fair elections. Those are likely to include appointing a neutral caretaker government and election commission.

Yet the opposition remains fractured. Mr. Sharif failed to persuade the members of the opposition alliance that he leads, the All Parties Democratic Movement, to adopt a united stand during a six-hour meeting on Sunday evening. With some smaller opposition parties still insisting on a boycott, the alliance could agree only to postpone the decision on a boycott and let those parties decide on their own.

Two parties, the religious Islamic Party and the Movement for Justice party of former cricket player Imran Khan, have said they will boycott the vote. Both have been strident critics of Mr. Musharraf.

The lawyers’ movement, which has led the calls for Mr. Musharraf’s resignation, has also urged parties to boycott unless the judiciary is restored. Four leading lawyers remain under house arrest, as do a large number of supreme and high court judges.

Aitzaz Ahsan, the main strategist behind the lawyers’ movement and a candidate for Parliament from Ms. Bhutto’s party, suggested in a letter that all candidates take an oath to work to restore the judiciary when elected.

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