Lawmakers voted Saturday in Pakistan's presidential election, with the scandal-tainted, pro-U.S. widower of slain ex-Prime Minister Benazir Bhutto expected to win easily.

If elected, Asif Ali Zardari, who also heads the main ruling party, could become one of the most powerful civilian leaders in Pakistan's turbulent 61-year history. Last month, he marshaled a coalition that forced longtime U.S. ally Pervez Musharraf to quit as head of state.

The election comes at a sensitive time for the nuclear-armed, Muslim nation of 160 million.

Pakistan's economy is crumbling and it faces rising violence by militants. The latter is a major concern of the U.S., which wants Pakistan to eradicate militant havens on its side of the border with Afghanistan. An American-led ground attack said to have killed at least 15 in Pakistani territory Wednesday sparked outrage and embarrassed Zardari's party.

Zardari faced off against Mushahid Hussain, a senator from the pro-Musharraf party routed in February parliamentary elections, and Saeed-uz-Zaman Siddiqui, a former judge nominated by the opposition party of another ex-prime minister, Nawaz Sharif.

Large numbers of security forces guarded the Parliament building in Islamabad on Saturday. Legislators in the four provincial assemblies also voted in the secret ballot.

Members of Zardari's Pakistan People's Party were optimistic.

"Our position is strong," said Amin Fahim, a senior party leader.

Like his late wife, Zardari is generally considered a pro-West liberal, and he is not expected to change Pakistan's commitment as an ally in the U.S. war on terrorism despite the recent raid and suspected U.S. missile strikes along the border.

Zardari and senior party lieutenants have matched Musharraf's tough line against terrorism, insisting the battle against Islamic militants is Pakistan's war. But a key test will be how much clout Zardari wields over Pakistan's powerful military, which has failed to halt the Taliban's rise in the nation's northwest despite stop-start battles.

The president has the power to dissolve Parliament and appoint army chiefs, and chairs the joint civilian-military committee that controls Pakistan's nuclear weapons.

Zardari and his party have promised to trim presidential powers — enhanced by constitutional changes under Musharraf — to bring them more in balance with Parliament and the prime minister. But it's unclear how far they will go. Questions also have come up about whether Zardari should keep his party leader position if he takes on the presidency.

A horse-loving aristocrat who has spent years in prison on corruption allegations, Zardari has impressed and surprised many with his ability to concentrate power since his wife was killed in a December gun-and-bomb attack and he inherited her party's leadership.

U.S. and other international leaders have watched his rise closely.

A Western diplomat said Zardari's ability to quickly get the support of smaller parties — after Sharif's group switched to the opposition last month — indicated the political scene could be more stable in coming months.

"He's put together a coalition that's pretty healthy," the diplomat said on condition of anonymity due to the sensitivity of the subject.

Political stability could be crucial to facing economic challenges that include soaring inflation, chronic power shortages and widening trade and budget deficits.

Zardari, the son of a landowning businessman and tribal chief from the southern province of Sindh, wed Bhutto in an arranged marriage in 1987. Many Pakistanis call him "Mr. 10 Percent," a reference to accusations he pocketed commissions on government contracts during her two terms as prime minister.

Zardari endured about 11 years in jail on corruption allegations but he was never convicted at home or in cases overseas. After Bhutto was killed, Zardari seized the reins of her party and led it to victory in the February elections.

Zardari's party and that of Sharif — historical rivals — formed a coalition whose main bond was a common hatred of Musharraf. Together they threatened to impeach the longtime leader, leading him to quit the presidency in mid-August.

A few days later, the coalition fell apart over disagreements about Musharraf's successor and how to restore judges he had sacked last year during a burst of emergency rule.

Sharif has said he would play a constructive role in the opposition, and one of his aides, Ahsan Iqbal, said Saturday that the party would accept whoever becomes president.

Iqbal nonetheless warned that the party would continue to push for the restoration of the judges, in particular deposed Chief Justice Iftikhar Mohammed Chaudhry. Zardari has accused Chaudhry of "playing politics" and called for sweeping judicial reforms expected to crimp the ability of the court to check the activities of the government.