ISLAMABAD, Pakistan - Pervez Musharraf, newly sworn in as a civilian president and minus his trademark general's uniform, promised Thursday to lift the state of emergency by Dec. 16 and restore Pakistan's constitution ahead of parliamentary elections.

If he keeps his word, Musharraf will have addressed key demands of opposition parties as well as the United States, an important supporter increasingly worried that Pakistani political turmoil could weaken the government's resolve to confront Islamic militants.

Musharraf urged opposition parties to participate in the election and help strengthen democracy, returning to his usually forceful persona after blinking back tears Wednesday when he resigned as commander of Pakistan's military and ended a 46-year army career.

"This is a milestone in the transition of Pakistan to the complete essence of democracy," he told officials, diplomats and generals at his oath-taking ceremony in the presidential palace. "Anyone who is talking of any boycotts should hear this out: Come hell or high water, elections will be held on Jan. 8. Nobody derails it."

Former Prime Minister Benazir Bhutto said her party, one of the country's two main opposition blocs, would compete in the election "under protest." She predicted the ballot would be rigged, but said it would be more dangerous to leave the election to pro-Musharraf parties.

Reflecting the anger at Musharraf and political uncertainty that have undercut the president's domestic and international support, the other key opposition leader, Nawaz Sharif, continued to urge a boycott as a way to attack the election's legitimacy.

Sharif, a bitter critic of Musharraf since the general ousted him as prime minister in a coup eight years ago, said he would try to persuade other parties to join him in a boycott -- a tough goal given the rivalry and animosities that divide Pakistan's many political groups.

A day after giving up the powerful post of military chief, Musharraf took the oath for a new five-year term as president, dapperly dressed in a long, dark tunic that contrasted with the medal-studded, khaki uniform he wore as a general.

He lauded his beloved army, defended his record and castigated foreign diplomats in the audience for their "obsession" with fast-tracking Pakistan to Western standards of democracy and human rights.

He didn't announce his plan for ending emergency rule, his first act as a civilian politician, for several hours, staring into a television camera during a sometimes halting address broadcast to the nation from his office.

"I am determined to lift the emergency by Dec. 16," Musharraf said, seated between a portrait of Pakistan's founding father, Mohammed Ali Jinnah, and a green-and-white national flag.

He urged Sharif and Bhutto not to boycott the parliamentary elections.

"A level playing field" is in place for the ballot and their parties should "participate fully," he said. "The elections, God willing, will be held free and transparent under the constitution."

Washington and London quickly welcomed the announcement.

"We hope that he follows through on that," White House press secretary Dana Perino said. "I think you have to give President Musharraf some credit here, because while he made the decision to establish the emergency order -- which we believed was a mistake, and we counseled against -- he did take the step" to lift it.

British Foreign Secretary David Miliband said London also looked forward to the lifting of the emergency and other restrictions -- one major television channel and several radio stations remain blocked and several judges and leading lawyers are still in custody.

"Both these steps are necessary so that all parties can participate fully and so that free and fair elections can take place," Miliband said.

Musharraf, 64, imposed emergency rule Nov. 3 in what he argues was a vital intervention to save Pakistan from political chaos and shore up its fight against rising Islamic militancy.

But there are serious doubts about his ability to survive for long in his new, less-powerful office.

Some observers say Musharraf was only able to decree a state of emergency because he had the support of his fellow generals, including Gen. Ashfaq Kayani, who became the military chief Wednesday.

If Musharraf continues to represent the military's interests, he could retain that backing and the authority to which he is accustomed. But some think Kayani wants to remove the army from the political spotlight and Musharraf will suffer for alienating not only the mainstream opposition but also the media and civil society groups such as lawyers.

In Lahore, street clashes broke out between police and lawyers protesting against Musharraf's inauguration, leaving four lawyers and three officers injured. Some 400 protesters chanted "Friends of Musharraf are traitors" and flung bricks and sticks at policemen.

With Musharraf weakened, Washington and other Western governments have been hedging their bets, reaching out to Bhutto and Sharif and stressing their friendship is with Pakistan, not just its embattled leader.

Mehdi Hasan, a Pakistani political analyst, said Musharraf should have responded to his sinking popularity by resigning months ago. He said the leader didn't really want to lift emergency rule because of worsening violence by militants -- a conflict that saw five soldiers killed and four wounded by a bomb Thursday in the tribal region along the Afghan border.

"The international community wanted him to do it (lift the emergency), and he had limited options because of the strength of the opposition, which is not ready to accept him even as a civilian president," Hasan said. "I foresee even worse turmoil in Pakistani politics."

Sharif has turned up the heat on Musharraf since his surprise return from Saudi Arabia on Sunday, insisting that judges fired under emergency rule must be reinstated for the elections to be meaningful.

Musharraf used his emergency decree to purge the Supreme Court, which was about to rule on the constitutionality of him winning October's presidential election by legislators while still holding a military post. A retooled high court, with justices appointed by Musharraf, gave its stamp of approval last week.

"Musharraf took oath today by murdering the judiciary," Sharif told reporters in the eastern city of Lahore.

He said his party and other smaller groups had decided in principle to boycott the ballot, but added a successful boycott would need the cooperation of Bhutto and others.

Bhutto, however, said her party would compete in the vote even though she alleged the ballot would not be conducted fairly.

"The dice is stacked against the opposition, but we feel that if we boycott, then the regime won't need to rig and the world will turn around and say the election was fair," she told the British Broadcasting Corp. "So it's important for us to mobilize the support we have and fight in the field."

But several senior members of her party said she had not completely abandoned the boycott option and would meet with Sharif to seek a common platform.