According to officials, Pakistan’s military leadership comes under unprecedented pressure from within its ranks to reduce ties with the United States. (AFP PHOTO/HO/ISPR)

The security relationship between the United States and Pakistan has sunk to its lowest level since the two countries agreed to cooperate after the Sept. 11, 2001, attacks, endangering counterterrorism programs that depend on the partnership, according to U.S. and Pakistani officials.

Both sides say further deterioration is likely as Pakistan’s military leadership comes under unprecedented pressure from within its ranks to reduce ties with the United States. The army chief, Gen. Ashfaq Kayani, was jeered last month by fellow officers who demanded in a town-hall-style meeting that he explain why Pakistan supports U.S. policy.

Kayani “is fighting to survive,” said one U.S. official, speaking on the condition of anonymity because of current sensitivities. “His corps commanders are very strongly anti-U.S. right now, so he has to appease them.”

Outspokenness to top officers is virtually unheard of in the strict Pakistani military hierarchy, and open criticism of Kayani “is something no Pakistani military commander has ever had to face before,” another U.S. official said. “Nobody should underestimate the pressure he’s now under.”

Tension over U.S.-Pakistani relations is building on the American side, as well. Lawmakers on Wednesday expressed outrage that a number of Pakistanis who had helped gather intelligence for the CIA about Osama bin Laden’s compound have been arrested.

Among them is Maj. Amir Aziz, a doctor in the Pakistani army’s medical corps who lived next to the bin Laden residence in Abbottabad for several years and has not been seen since shortly after the raid by U.S. commandos in early May that killed the terrorist leader.

Officials said Aziz was among several Pakistanis paid to keep track of and photograph those entering and leaving the compound, without being told whom they were looking for.

“Their families don’t have any idea where they have been taken,” said one neighbor in Abbottabad’s Bilal Town subdivision. “Nobody knows what they had done.”

A U.S. official said the CIA tried to get the doctor and other informants out of harm’s way before their arrests, offering to relocate them. But they refused and “thought they would be okay,” the official said, speaking on the condition of anonymity to discuss intelligence matters. A Pakistani military spokesman said reports that an officer had been detained were “totally baseless.”

After years of sporadic tension between Washington and Islamabad, the immediate cause of the rupture was the raid on bin Laden’s compound, located minutes from Pakistani military installations. Pakistan was not informed before the operation, a level of secrecy that left its military and intelligence services angry and humiliated.

In recent weeks, Pakistanis have escalated their demands that the United States stop its covert campaign of drone strikes on al-Qaeda and Afghan Taliban bases in the country’s tribal areas, and at least some U.S. personnel are being withdrawn from a base in the southwest part of the country used by the CIA to launch the unmanned aircraft. A U.S. Special Operations training program for Pakistan’s tribal defense force has largely ceased. Visas have been withheld from CIA and military personnel assigned to Pakistan programs, according to officials from both countries.

Pakistan is a key player in the administration’s war strategy in Afghanistan, but U.S. officials are under similar pressure at home to take a tough line. Many in Congress see bin Laden’s presence in Pakistan and the fallout from the raid as additional proof that the Pakistanis are unreliable partners who refuse to fully commit to fighting insurgents and do not deserve U.S. assistance or trust. U.S. military and economic assistance to Pakistan, although only a small fraction of the overall cost of the Afghanistan war, has totaled nearly $21 billion since 2002.

Last week, Defense Secretary Robert M. Gates acknowledged that U.S. intelligence that had been given to Pakistan in mid-May about insurgent bomb factories in the tribal regions was leaked, and that the facilities were abandoned before military strikes could take place.

In a congressional hearing Wednesday with Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, Sen. Patrick J. Leahy (D-Vt.) said, “Just this morning, we see word that our putative ally arrested five people under the suspicion that they helped the United States to get Osama bin Laden, after publicly saying, of course, they wanted us to get Osama bin Laden.”

“Most governments lie to each other,” Gates responded tersely. “That’s the way business gets done.” Even some of the United States’ closest allies, he said, “send people to spy on us. . . . That’s the real world we deal with.”

Mullen warned against pushing the Pakistanis too hard. The relationship is a challenge, he agreed, and “some of the criticism is more than warranted.” But “if we walk away from it, it’s my view it’ll be a much more dangerous place a decade from now, and we’ll be back.”

U.S. officials said they took some comfort in the fact that, despite the strong public rhetoric in Pakistan, a series of meetings with high-level Pakistani officials since the bin Laden raid has been frank and productive. Mullen; Secretary of State Hillary Rodham Clinton; Gen. James N. Mattis, head of U.S. Central Command; and CIA Director Leon Panetta have all traveled there in recent weeks.

The Pakistanis have responded positively to some U.S. demands, including granting the CIA access to the Abbottabad compound and to bin Laden family members in Pakistani detention. On the civilian side, Prime Minister Yousaf Raza Gillani this week publicly called for a resumption of the U.S.-Pakistan strategic dialogue, suspended several months ago, following meetings with Deputy Secretary of State Thomas R. Nides. Before leaving Islamabad on Tuesday, Nides announced disbursement of $190 million in U.S. aid for Pakistani flood victims.

But there are few illusions on either side about the depth of the chasm between them. The bin Laden raid followed other incidents that infuriated the Pakistani military, including WikiLeaks’ publication of State Department cables recounting private conversations between U.S. officials and Kayani, and the U.S.-demanded release of Raymond Davis, a CIA contractor accused of killing two Pakistanis in Lahore in January.

The drone campaign is under particular challenge. Last month, Pakistan’s Parliament passed a resolution calling for an immediate end to the strikes. Last week, the military issued a statement that called them “not acceptable under any circumstances. There is no room for ambiguity in this regard.”

U.S. officials say they could continue without Pakistan’s cooperation, launching the drones out of bases in Afghanistan. But there is a fear that the instability and high feelings in Pakistan could provoke an even more extreme public and military backlash.

Even before the current tensions, Pakistan criticized the program, expanded by the Obama administration to nearly 120 strikes last year, for targeting too many low- and mid-level militants rather than high-level commanders. The Americans, a senior Pakistani military official said, are fixated on drones and use them as indiscriminately as “a rifle bullet.”

The most recent drone strikes took place Wednesday in North and South Waziristan in the tribal areas, where local officials said 15 militants were killed.

Witte reported from Islamabad. Staff writer Greg Miller in Washington and special correspondents Shaiq Hussain in Islamabad and Haq Nawaz Khan in Peshawar contributed to this report.