JUSTIFYING his decision to resign Monday, Pakistan President Pervez Musharraf said he hoped to avoid a long political crisis triggered by an attempt by the governing coalition to start impeachment proceedings against him. While he may be right on that score, his resignation could plunge an already unstable nation into even greater turmoil.

Since February's election, the winning parties have used Musharraf's presidency as an excuse for their failure to agree on a coherent government policy. With him gone, they'll have no such excuse for inaction and sterile maneuvering. That, in turn, could weaken their fragile popular base and revitalize the Islamist parties who were mauled in the election.

The main coalition partners, the Muslim League (MLN) and the Pakistan People Party (PPP), hate each other nearly as much as they hate Musharraf.

The PPP's base is Sind province; the MLN's is Punjab. The two provinces, Pakistan's most populous, have a long history of rivalry and are sure to want the presidency for their rival favorite sons. The PPP's effective leader, Asif Ali Zardari, is from Sind; the MLN's chairman, Nawaz Sharif, is a Punjabi. Both may be tempted to seek the presidency.

One reason: Neither is likely to be acceptable as prime minister to a majority of Pakistanis. With few qualifications apart from having been the husband of the murdered ex-Premier Benazir Bhutto, Zardari lacks the experience to lead a government. Sharif, although twice prime minister, is too tainted by corruption charges and shady business deals.

The parliament must elect the new president within 30 days - but, as things stand now, neither Zardari nor Sharif could secure enough votes to get the post. The bloc of parliamentarians who've remained loyal to Musharraf could decide the outcome.

The PPP and the MLN have promised to amend the constitution to revert to a parliamentary system, with real executive power in the hands of the prime minister backed by a majority in the lower house. But then they'd have to replace Prime Minister Yusuf Gilani, who's always been regarded as a straw man. The fight over who succeeds him could tear the coalition asunder.

The PPP and MLN are in what looks like a last-chance saloon. A majority of Pakistanis voted them back into power on the understanding that they'd maintain the nation's stability while continuing the process of democratization. But they've spent the last six months trying to force out Musharraf.

Now they may seek other diversions - demagogic tricks such as rehabilitating A.Q. Khan, the so-called Father of the Pakistani Nuclear Bomb, and the man who sold atomic technology and equipment to Iran, Libya and North Korea.

Worse, they might release thousands of Pakistani Taliban terrorists on the pretext that they were "victims of Musharraf's dictatorship." After all, the Taliban was originally created in 1994 - when the PPP was in power in Islamabad. It continued to enjoy Pakistani support when the MLN was in government.

Any attempt to soften Musharraf's stand against Islamist terrorism (which Washington already deemed too soft) could encourage the Taliban and its al Qaeda allies - especially in Afghanistan, where the war seems to be getting hotter by the day.

The PPP and MLN have also made it clear they wish to cool down relations with America, which they see as an unreliable ally whose policies could radically change depending on who wins the White House. The Bush administration's decision not to utter a word in support of Musharraf (the man who took the strategic decision to turn Pakistan into a US ally in 2001), plus the chorus of attacks on him in the US media, confirmed that impression.

The two parties have always regarded China as Pakistan's chief ally, especially against India, which many Pakistanis see as an existential threat to their Islamic state. After the Olympics, China might end its policy of "minimum involvement in foreign affairs" and seek a more direct say in what happens in Pakistan - which it has long regarded as part of its zone of influence.

Watching all these developments would be Gen. Ashfaq Kayani, who succeeded Musharraf as Army chief of staff. A US-trained professional soldier, Kayani has shown no signs of a taste for politics. Yet one never knows when Pakistani generals might decide to reclaim political control.

In all this, America still has a say - if only because it has pumped more than $10 billion of military aid into the Pakistani armed forces and equipped them with state-of-the-art F-16 fighter bombers that can carry Islamabad's nuclear warheads into a good part of Southwestern Asia and the Middle East.

The Bush administration played a crucial role in helping to restore democracy to Pakistan. But it hasn't devised a policy to deal with the more complex situation that the return to democracy has created.