ISLAMABAD, PAKISTAN - One of the two main parties in Pakistan's ruling coalition declared Monday it would quit the government in a dispute over when and how to reinstate judges fired by President Pervez Musharraf during a crackdown late last year.

The announcement by former Prime Minister Nawaz Sharif, leader of the Pakistan Muslim League-N faction, raises the prospect of a messy splintering of the alliance that soundly defeated the party of the U.S.-backed Musharraf at the polls nearly three months ago.

Sharif said his party, although relinquishing its Cabinet posts, would continue to support the coalition for the time being, and negotiations between the two parties were expected to continue. But the turn of events suggested it would be difficult for them to stay together in the longer term and forge a common policy on pressing matters such as confronting Islamic militants.

The biggest share of votes in February's parliamentary election was won by the Pakistan People's Party, led by Benazir Bhutto until her assassination Dec. 27. Her husband, Asif Ali Zardari, stepped in as leader after her death.

The party of Sharif, who like Bhutto spent years in exile under Musharraf, took the second-largest share, and the two groups agreed to join forces despite some major philosophical differences. Most of their affinity appeared based on a mutual distaste for Musharraf, who seized power in a 1999 coup and has seen his popularity plunge over the last year.

Musharraf fired the popular chief justice, Iftikhar Chaudhry, and about 60 other judges in November, when the president also declared a state of emergency. The dismissals fed widespread protests and hurt the ruling party at the polls.

The dispute over the reinstatement of judges points up the larger question of whether Musharraf should be allowed to continue to serve as a figurehead president or be forced out. Sharif has demanded his ouster, while Zardari has signaled willingness to work with the president, as long as his powers are largely ceremonial.

At the time Musharraf declared emergency rule, Chaudhry's Supreme Court had appeared poised to invalidate his re-election by the outgoing Parliament last year. If reinstated, the chief justice once again could take up legal challenges to Musharraf's new five-year term.

Sharif and Zardari have been quarreling for weeks now about the judges. The new government pledged when it took power six weeks ago that the judges would be restored by an act of Parliament within a month.