WASHINGTON - 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 signals a new U.S. resolve to decapitate the Taliban. But it also risks rupturing the U.S. relationship with Pakistan.

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, say that attacking the Taliban in Quetta, or threatening to do so, is vital to the success of the new war strategy President Obama announced 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. "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, are 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. If the United States were to follow 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 drones in rural tribal areas along the Afghan border. The operations have been conducted with the consent of President Asif Ali Zardari's government.

But Zardari faces mounting political woes, and the CIA strikes 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 likely increase.

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

But the push to expand drone strikes underscores the limits of the 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 had not issued 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," a U.S. counterterrorism official said.

In the last two years, the CIA has carried out dozens of air strikes, killing at least 10 al-Qaeda operatives.