ISLAMABAD, Pakistan - President Gen. Pervez Musharraf pushed ahead Tuesday with plans for his expected re-election as president, naming a trusted ally to lead the military in his place and agreeing to amnesty for a former prime minister who could become a key ally.

Musharraf has enraged opponents by simultaneously serving as head of the army and president but has promised to doff his uniform if he wins Saturday's vote by national and provincial legislatures. However, a bloc of opposition legislators resigned from parliament on Tuesday, hoping their departure would rob the election of legitimacy.

Musharraf will also grant former prime minister Benazir Bhutto and others amnesty as early as Wednesday in various corruption cases, said Deputy Information Minister Tariq Azim. The amnesty was one of Bhutto's key demands during power-sharing negotiations, which Azim said resumed Tuesday.

Bhutto plans to return to Pakistan from London on Oct. 18, eight years after she went into self-imposed exile to escape prosecution.

Azim said the amnesty was aimed at easing political acrimony ahead of parliamentary elections due by January. He indicated that it would also apply to former prime minister Nawaz Sharif, whose government was ousted in the 1999 coup that brought Musharraf to power.

"I think in that spirit of national reconciliation we have to go through this,'' Azim said.

Bhutto has been charged in Pakistan with illegally amassing properties and bank accounts overseas while in power. She was also convicted of money laundering in Switzerland in July 2003 and ordered to pay $11 million to the Pakistani government. The conviction was automatically thrown out when she contested it, but the case is still under investigation.

Governing party officials have urged Bhutto's party not to join other opposition parties in boycotting Saturday's ballot, though Musharraf's allies insist they have enough votes to win in any case.

"We have to hold the presidential election to meet a constitutional requirement and we will do it,'' Information Minister Mohammed Ali Durrani said.

Maulana Fazal-ur Rahman, leader of the opposition in parliament, said Musharraf might win but his victory would lack legitimacy. "After our resignation, Musharraf's success would have no value,'' Rahman said.

Musharraf, who seized power in a 1999 coup, has faced growing opposition since March when he made a botched attempt to oust the country's chief justice.

Gen. Ashfaq Kiani, a former intelligence chief, will become vice chief of the army on Monday and will take the powerful top job when Musharraf vacates it, a military statement said.

Lawyers for Musharraf's two main rivals in Saturday's vote -- retired judge Wajihuddin Ahmed and Makhdoom Amin Fahim, vice-chairman of the Bhutto's party -- filed two petitions with the Supreme Court on Tuesday.

Both argue that Musharraf is ineligible to run because he has retained his role as army chief and that the Election Commission was wrong to approve his nomination papers Saturday.

The court dismissed several similar challenges Friday, but lawyers hoped it would act after the commission changed an election rule in Musharraf's favour.

"We have a strong case against Pervez Musharraf,'' lawyer Tariq Mahmood told reporters.

The opposition also insists Musharraf should not seek re-election by the current assemblies, but should wait until after new legislative elections.

Opposition leaders have submitted the resignations of all 85 of their legislators in the 342-seat National Assembly. Two ruling party legislators also quit over their differences with their party's policies.

"Our lawmakers are making this sacrifice in the larger interest of Pakistan. It is a decisive moment,'' said Javed Hashmi, acting leader of Sharif's Pakistan Muslim League-N party.

Under the constitution, the president is elected by the National Assembly, the Senate and the four provincial legislatures. The opposition submitted mass resignations Monday in three of the provincial assemblies and planned to do so later in the fourth.

Both Musharraf, a close U.S. ally, and Bhutto have called for moderates to unite against extremism. Bhutto said Monday she would co-operate with the American military in targeting al Qaeda leader Osama bin Laden.

Authorities have resorted to authoritarian methods to contain the opposition, including using tear gas and batons Saturday on lawyers protesting against Musharraf. On Monday, Chief Justice Iftikhar Mohammed Chaudhry ordered three officials suspended over the crackdown that injured dozens, including journalists covering the demonstration.