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

The announcement by a former prime minister, Nawaz Sharif, the 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 American-backed Mr. Musharraf at the polls nearly three months ago.

Mr. 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 December 27. Her husband, Asif Ali Zardari, stepped in as leader after her death, with the couple’s college-student son, Bilawal, as co-chairman.

The party of Mr. Sharif, who like Bhutto spent years in exile under Mr. 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 Mr. Musharraf, who seized power in a 1999 coup and has seen his popularity plunge over the last year.Mr. 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, hurting the party at the polls.

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

At the time Mr. Musharraf declared emergency rule, Mr. 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 Mr. Musharraf’s new five-year term.