"Planning has been reinvigorated in the wake of Times Square," one of the officials said.

At the same time, the administration is trying to deepen ties to Pakistan's intelligence officials in a bid to head off any attack by militant groups. The United States and Pakistan have recently established a joint military intelligence center on the outskirts of the northwestern city of Peshawar, and are in negotiations to set up another one near Quetta, the Pakistani city where the Afghan Taliban is based, according to the U.S. military officials. They and other officials spoke on the condition of anonymity because of the sensitivity surrounding U.S. military and intelligence activities in Pakistan.

The "fusion centers" are meant to bolster Pakistani military operations by providing direct access to U.S. intelligence, including real-time video surveillance from drones controlled by the U.S. Special Operations Command, the officials said. But in an acknowledgment of the continuing mistrust between the two governments, the officials added that both sides also see the centers as a way to keep a closer eye on one another, as well as to monitor military operations and intelligence activities in insurgent areas.

Obama said during his campaign for the presidency that he would be willing to order strikes in Pakistan, and Secretary of State Hillary Rodham Clinton said in a television interview after the Times Square attempt that "if, heaven forbid, an attack like this that we can trace back to Pakistan were to have been successful, there would be very severe consequences."

Obama dispatched his national security adviser, James L. Jones, and CIA Director Leon Panetta to Islamabad this month to deliver a similar message to Pakistani officials, including President Asif Ali Zardari and the military chief, Gen. Ashfaq Kiyani.

Jones and Panetta also presented evidence gathered by U.S. law enforcement and intelligence agencies that Shahzad received significant support from the Pakistani Taliban.

The U.S. options for potential retaliatory action rely mainly on air and missile strikes, but could also employ small teams of U.S. Special Operations troops already positioned along the border with Afghanistan. One of the senior military officials said plans for military strikes in Pakistan have been revised significantly over the past several years, moving away from a "large, punitive response" to more measured plans meant to deliver retaliatory blows against specific militant groups.

The official added that there is a broad consensus in the U.S. military that airstrikes would at best erode the threat posed by al-Qaeda and its affiliates, and risk an irreparable rupture in the U.S. relationship with Pakistan.

"The general feeling is that we need to be circumspect in how we respond so we don't destroy the relationships we've built" with the Pakistani military, the second official said.

U.S. Special Operations teams in Afghanistan have pushed for years to have wider latitude to carry out raids across the border, arguing that CIA drone strikes do not yield prisoners or other opportunities to gather intelligence. But a 2008 U.S. helicopter raid against a target in Pakistan prompted protests from officials in Islamabad who oppose allowing U.S. soldiers to operate within their country.

The CIA has the authority to designate and strike targets in Pakistan without case-by-case approval from the White House. U.S. military forces are currently authorized to carry out unilateral strikes in Pakistan only if solid intelligence were to surface on any of three high-value targets: al-Qaeda leaders Osama bin Laden and Ayman al-Zawahiri, or Taliban chief Mohammad Omar. But even in those cases, the military would need higher-level approval.

"The bottom line is you have to have information about targets to do something [and] we have a process that remains cumbersome," said one of the senior military officials. "If something happens, we have to confirm who did it and where it came from. People want to be as precise as possible to be punitive."

U.S. spy agencies have engaged in a major buildup inside Pakistan over the past year. The CIA has increased the pace of drone strikes against al-Qaeda affiliates, a campaign supported by the arrival of new surveillance and eavesdropping technology deployed by the National Security Agency.

The fusion centers are part of a parallel U.S. military effort to intensify the pressure on the Taliban and other groups accused of directing insurgent attacks in Afghanistan. U.S. officials said that the sharing of intelligence goes both ways and that targets are monitored in both Afghanistan and Pakistan.

In the Peshawar fusion cell, which was set up within the last several months, Pakistanis have access to "full-motion video from different platforms," including unarmed surveillance drones, one official said.

The fusion centers also serve a broader U.S. aim: making the Pakistanis more dependent on U.S. intelligence, and less likely to curtail Predator drone patrols or other programs that draw significant public opposition.

To Pakistan, the fusion centers offer a glimpse of U.S. capabilities, as well as the ability to monitor U.S. military operations across the border. "They find out much more about what we know," one of the senior U.S. military officials said. "What we get is physical presence -- to see what they are actually doing versus what they say they're doing."

That delicate arrangement will be tested if the two sides reach agreement on the fusion center near Quetta. The city has served for nearly a decade as a sanctuary for Taliban leaders who fled Afghanistan in 2001 and have long-standing ties to Pakistan's powerful Inter-Services Intelligence directorate.

U.S. officials said that the two sides have done preliminary work searching for a suitable site for the center but that the effort is proceeding at a pace that one official described as "typical Pakistani glacial speed." Despite the increased cooperation, U.S. officials say they continue to be frustrated over Pakistan's slow pace in issuing visas to American military and civilian officials.

One senior U.S. military official said the center would be used to track the Afghan Taliban leadership council, known as the Quetta shura. But other officials said the main mission would be to support the U.S. military effort across the border in Kandahar, Afghanistan, where a major U.S. military push is planned.

*Staff writers Greg Jaffe and Karen DeYoung contributed to this report.