WASHINGTON — All eyes will be on Pakistan’s former premier, Nawaz Sharif, after his announcement yesterday that he is pulling his party out of the government, rupturing the coalition of political parties that effectively drove President Musharraf from power.

Despite vowing to play a constructive role in his country’s politics, Mr. Sharif is believed by most experts to be biding his time and waiting for new parliamentary elections after the presidential contest next month to make his political comeback. Such a return to power could complicate American-Pakistani relations, as Mr. Sharif has historical ties to Al Qaeda and the Taliban, two terrorist groups the countries are fighting in the tribal frontier provinces along the Afghan border.

Mr. Sharif’s withdrawal of his Pakistan Muslim League-Nawaz party from the coalition leaves Asif Ali Zardari, widower of another former premier, Benazir Bhutto, in control of a government battling Al Qaeda and the Taliban. Mr. Zardari, head of the Pakistan Peoples Party, announced yesterday that he would ban from political participation the Taliban, which claimed responsibility for two suicide bombings against a Pakistani military installation last week that left 67 people dead.

Both American and former Pakistani officials allege that Mr. Sharif has had long-standing ties to Osama bin Laden and Al Qaeda. In 2005, a former Pakistani intelligence official, Khalid Khawaja, told the Asia Times that he arranged three meetings in Saudi Arabia between Mr. Sharif and Mr. bin Laden, a claim Mr. Sharif denied.

An American intelligence official told The New York Sun yesterday that a white paper on Islamist penetration of the Pakistani military and intelligence services, delivered earlier this month to senior Pakistani military and political leaders, says Mr. Sharif continues to receive some funding from the Taliban and Al Qaeda. “It’s not like they are bankrolling his entire campaign, but they pay him a large sum of money,” the official said.

In an interview yesterday, a former senior State Department South Asia specialist, Daniel Markey, acknowledged that Mr. Sharif had “connections” to Al Qaeda in the 1990s. But he said it would be incorrect to call the former premier an Islamist.

“I don’t believe Nawaz Sharif should be called an Islamist,” Mr. Markey, who is now a scholar at the Council on Foreign Relations, said. “I think at times in the 1990s he was connected to bin Laden, but we have to put this in the historical context. Now we need to be concerned that he might continue to have ties to people clearly not interested in working with the United States, but at this point those people would not include Al Qaeda. At the same time, he has yet to see the fight against terrorism as a fight his party should take up.”

Another former State Department Pakistan analyst, Marvin Weinbaum, said he was not worried that a future Sharif government would cut off cooperation with America. Indeed, Mr. Weinbaum said he interviewed members of Mr. Sharif’s party in October and that they pledged to work closely with America if their party gained power.

“Sharif’s connections are to the religious parties and the religious establishment that has been part of the political system,” Mr. Weinbaum, a scholar at the Middle East Institute, said. “He has no connections to people who would be considered terrorists. Before he was ousted by Musharraf” — as prime minister, in 1999 — “he was in discussions with the United States, and working together with our intelligence community to go after Al Qaeda.”

Those discussions have been noted by former American intelligence and counterterrorism officials. One of those officials, Bruce Riedel, who served as President Clinton’s director for the Middle East and Southeast Asia on the National Security Council, described Mr. Sharif’s cooperation as “promises, promises.” Mr. Riedel said yesterday, however, that he does not consider Mr. Sharif to be connected in a meaningful way to Al Qaeda.

“Nawaz Sharif is not an Islamic extremist. We worked with him twice in the 1990s. His government did not deliver everything we asked for. I don’t think we should demonize this man, though,” Mr. Riedel, a scholar at the Brookings Institution, said. “It is well worth remembering that it was Benazir Bhutto’s government that first started working to help create the Taliban. There is no Pakistani leader in our lifetime who has not had connections to Islamists.”