Senior U.S. officials are pushing to expand CIA drone strikes beyond Pakistan's tribal region and into a major city in an attempt to pressure the Pakistani government to pursue Taliban leaders based in Quetta.

The proposal has opened a contentious new front in the clandestine war. The prospect of Predator aircraft strikes in Quetta, a sprawling city, signals a new U.S. resolve to decapitate the Taliban. But it also risks rupturing Washington's relationship with Islamabad.

The concern has created tension among Obama administration officials over whether unmanned aircraft strikes in a city of 850,000 are a realistic option. Proponents, including some military leaders, argue that attacking the Taliban in Quetta -- or at least threatening to do so -- is crucial to the success of the revised war strategy President Obama unveiled last week.

"If we don't do this -- at least have a real discussion of it -- Pakistan might not think we are serious," said a senior U.S. official involved in war planning. "What the Pakistanis have to do is tell the Taliban that there is too much pressure from the U.S.; we can't allow you to have sanctuary inside Pakistan anymore."

But others, including high-ranking U.S. intelligence officials, have been more skeptical of employing drone attacks in a place that Pakistanis see as part of their country's core. Pakistani officials have warned that the fallout would be severe.

"We are not a banana republic," said a senior Pakistani official involved in discussions of security issues with the Obama administration. If the United States follows through, the official said, "this might be the end of the road."

The CIA in recent years has stepped up a campaign against Al Qaeda and the Taliban in Pakistan, much of it with drone strikes in the rural tribal areas along the border with Afghanistan. The operations have been conducted with the consent of the government of President Asif Ali Zardari, who has proved a reliable ally to America in his first 15 months in office.

Zardari, however, is facing mounting political woes, and the CIA airstrikes are highly unpopular among the Pakistani public, because of concerns over national sovereignty and civilian casualties. If drone attacks now confined to small villages were to be mounted in a sizable city, the death rate of innocent bystanders would probably increase.

Obama has endorsed an expansion of CIA operations in the country, approving the deployment of more spies and resources in a clandestine counterpart to the 30,000 additional U.S. troops being sent into Afghanistan.

But the push to expand drone strikes underscores the limits of the Obama offensive. The administration has given itself 18 months to show evidence of a turnaround in Afghanistan. But progress in Pakistan depends almost entirely on drone strikes and prodding a sometimes reluctant ally, which provides much of the intelligence to conduct the strikes, to do more.

U.S. and Pakistani officials stressed that the United States has stopped short of issuing an ultimatum to Pakistan. "It just doesn't make a whole lot of sense to use heavy-handed tactics when you've got this kind of relationship," said a U.S. counter-terrorism official. Like others, he discussed the issue on condition of anonymity because of the sensitivity of the subject.

Obama alluded to the effort to enlist more Pakistani help on the day his strategy was announced.

"The most important thing we can do in Pakistan is to change their strategic orientation," Obama said in a meeting with news columnists Dec. 1. The pursuit of Al Qaeda involves a range of activities, he said, "some of which I can't discuss."

As Obama deliberated over the strategy for Afghanistan through fall, administration officials consulted with Pakistan in high-level meetings in Islamabad, also using those sessions to pressure the government to do more.

Among those involved were Gen. James L. Jones, Obama's national security advisor; Gen. Stanley A. McChrystal, the U.S. commander in Afghanistan; and Leon E. Panetta, director of the CIA.

"We have applied enormous pressure," the senior U.S. official said.

Pakistan is not expected to hand over Mullah Mohammed Omar, the Taliban leader and longtime ally of Osama bin Laden who fled Afghanistan when U.S. forces invaded after the Sept. 11 attacks. Omar is believed to have used Quetta as a base from which to orchestrate insurgent attacks in Afghanistan.

But U.S. officials said they have presented Pakistan with a list of Taliban lieutenants and argued that, with a U.S. pullout scheduled to begin in 18 months, the urgency of dismantling the so-called Quetta shura is greater than at any time in the 8-year-old war.

The senior Pakistani official bristled at the suggestion that Pakistan has been reluctant to target militants in Quetta, saying U.S. assertions about the city's role as a sanctuary have been exaggerated.