Islamabad, Pakistan — President Musharraf faced the gravest challenge of his nine-year rule yesterday when Pakistan’s coalition government announced the onset of impeachment proceedings.

The move threatened more turmoil in the nuclear-armed country, which America counts as an important ally in the “war on terrorism.”

Mr. Musharraf, who seized power in a bloodless coup in 1999, was consulting aides over his options. He could either force new elections by dissolving parliament, or declare a state of emergency.

The leader of the Pakistan People’s Party and the most powerful figure in the ruling coalition, Asif Ali Zardari, said Mr. Musharraf had “eroded the trust of the nation.” He added: “We have good news for democracy. The coalition believes it is imperative to move for impeachment against General Musharraf.”

Mr. Zardari spoke at a news conference flanked by the leader of the Pakistan Muslim League – Nawaz and the second most powerful member of the coalition, Nawaz Sharif.

Mr. Zardari accused the president of failing to honor promises to step down, of wrecking Pakistan’s economy through the “incompetence and failure of his policies,” and of trying to undermine the new coalition government.

Mr. Musharraf showed the seriousness of the threat by canceling a planned trip to the opening ceremony of the Beijing Olympics.

Parliament will now be recalled and proceedings could begin on Monday. It would be the first attempt to impeach a president in Pakistan’s 61-year history.

Mr. Musharraf’s opponents need a two-thirds majority in the upper and lower houses — 295 votes of the 439 — to remove him.

Together, the PPP and PML-N have 266 seats. They will need another 26 members of Parliament from the Tribal Areas bordering Afghanistan and three independents to carry the impeachment motion. Traditionally, MPs from the Tribal Areas vote for whoever pays them the most. The presidential camp is hoping to persuade these members to back Mr. Musharraf.

The president, who stepped down as army commander and is now a civilian, has been isolated since the PPP and the PML-N won a general election in February.

Mr. Musharraf’s allies warned that he would fight to stay in power. In his memoirs, the president describes himself as a “dada gear” — Urdu for “tough guy.” One close aide said: “The president is a sore loser. Remember that.”

Another added that his options were “either to issue an order dissolving the National Assembly or impose emergency rule, under which the government will be suspended and a new caretaker set-up would be announced.”

The army’s reaction will also be crucial. General Ashfaq Pervez Kiyani, who succeeded Mr. Musharraf as army chief last November, has tried to keep the military out of politics but has always been loyal to the president. The army’s powerful corps commanders met yesterday, but officials did not say if they discussed the impeachment.

A US State Department spokesman said the impeachment move was an “internal” matter for the Pakistanis to decide.

Pakistani observers are divided over whether the president will survive.

A local commentator, Shafqat Mahmood, said Mr. Musharraf could no longer count on the army’s support if he imposed emergency rule or dissolved parliament.

“If the coalition have the numbers, Musharraf is a gone person,” he said.