Hopes for much-needed political stability in Pakistan have crumbled along with its ruling coalition. Following Nawaz Sharif's exit from the government Monday, the political stage looks set to be dominated by a power struggle, which will draw attention away from antimilitant efforts and a faltering economy.

Only a week after it celebrated the resignation of former president Pervez Musharraf, Pakistan's fractious coalition broke when former prime minister Mr. Sharif, leader of the Pakistan Muslim League-Nawaz (PML-N), stormed out on the Pakistan People's Party (PPP). He blames his former coalition partner for repeatedly reneging on its promise to reinstate 60 judges suspended by Mr. Musharraf last year.

Sharif was also angered by an announcement that Asif Ali Zardari, chairman of the PPP and widower of its former leader, Benazir Bhutto, would stand for president. The coalition partners had agreed to back a nonpartisan candidate until the presidents' powers were constitutionally pared down.

Observers had hoped Mr. Zardari and Sharif, who represent different constituencies, would counterbalance each other. But Zardari looks set to grab as much power as he can while Sharif will seek to undermine him in opposition.

In the 1990s, Sharif and the PPP, under Ms. Bhutto, were bitter rivals and alternated terms in power. Many Pakistanis dread a return to the rancor and chaos of those days, which resulted, in 1999, in Musharraf's bloodless coup.

The split is unlikely to prompt early elections because the PPP, which holds the most seats in parliament, but not a majority, should be able to attract the support of smaller parties.

Instead, the rivalry between the two men is likely to be played out in presidential elections, scheduled for Sept. 6. In response to Zardari's nomination, Sharif has named his party's candidate: Saeed-uz-Zaman Siddiqui, a former chief justice.

Political pundits will also be keeping a close watch on the Punjab, Pakistan's biggest and most politically influential province. The PML-N has ruled the Punjab with the PPP, but without its support, it may be reduced to a minority.

Sharif will thus be looking to rally support, particularly among members of the PML-Quaid-e-Azam (PML-Q), which splintered from the PML-N after Sharif was ousted in 1999 and then backed Musharraf. The PML-Q knows its best bet in the national elections lies with Sharif, who remains the most popular politician.

Sharif is also likely to seek and score political points from Zardari's refusal to reinstate the judges, a position that has caused anger and disappointment throughout Pakistan. Talat Hussain, a political commentator and leading journalist, says the PPP could demonstrate that it would lead a stable government by immediately restoring the judges, "but Mr. Zardari has shown himself unwilling to do that."

Zardari, who is likely to win the presidency next week, is believed to oppose the return of the judges because he fears they will repeal an amnesty on corruption charges granted him last year. The former businessman has served more than eight years in prison on corruption and other criminal charges, but without being convicted.

Concerns about Zardari's likely presidency extend beyond corruption charges. "Zardari is a very unpredictable guy," says Mr. Hussain, referring to the fact that Zardari apologized to Sharif on state television Monday night and asked him to rejoin the government. "What kind of politics is he playing? That kind of inconsistency will be very bad for Pakistan."

The United States, however, is believed to be more comfortable with the prospect of working with Zardari than with Sharif, who is remembered as a difficult prime minister during the 1990s. A conservative Muslim with even more conservative followers, Sharif has said that he is intent on quashing militancy but would like to lower the profile of US involvement in the war on terror.

Zardari, by comparison, has adopted a hawkish tone in recent days, arguing that the Pakistani Taliban should be banned. Analysts say that regardless of his political battle with Sharif, Zardari will have to demonstrate convincingly that he is taking control of Pakistan's fight against terrorism if he is to enjoy any credence as president.