RAWALPINDI, Pakistan—In what could be the biggest change in a decade in a relationship that has been a mainstay of U.S. military and counterterrorism policy since the 9/11 terror attacks, the United States and Pakistan are lowering expectations for what the two nations will do together and planning for a period of more limited contact.

The change described by both Pakistani and U.S. officials follows a series of diplomatic crises over the past year that strained an already difficult partnership based around the U.S. goal of stability in Afghanistan and Pakistan and a reduction in Islamic-inspired terrorism.

For Pakistan, cooperation on that agenda was rewarded with billions in financial aid. The change means less cooperation with Washington and a willingness to swear off some aid that often made Pakistan feel too dependent, and too pushed around.

For the United States, scaling down an expensive military and economic program that has not met expectations could come at the cost of less Pakistani help in ending the war in next-door Afghanistan.

Both U.S. and Pakistani officials said the November killing of 24 Pakistani soldiers in a NATO airstrike and Washington's refusal to outright apologize for the deaths has been a game changer in a relationship characterized by mistrust and mutual acrimony.

In the United States, civilian and military officials have called the friendly fire incident a tragedy caused by mistakes on both sides, but insist that Pakistan fired first. Pakistan denies that, and has called the incident an unprovoked attack.

Pakistan's loudly angry reaction has, if anything, hardened attitudes in Congress and elsewhere that Islamabad is untrustworthy or ungrateful.

A senior Obama administration official conceded that the deaths made every aspect of U.S. cooperation with Pakistan more difficult, and that the distance Pakistan has imposed may continue indefinitely. The official, like most others interviewed for this story, spoke on condition of anonymity because of the sensitivity of ongoing discussions.

Pakistan has already stopped billing the United States for its anti-terror war expenses under the 10-year-old Coalition Support Fund, set up by Washington after the 9/11 attacks to reimburse its many allies for their military expenses fighting terrorists worldwide and touted by the U.S. as a success story.

"From here on in we want a very formal, business- like relationship. The lines will be drawn. There will be no more of the free run of the past, no more interpretation of rules. We want it very formal with agreed upon limits," military spokesman Gen. Athar Abbas told The Associated Press in an interview in the garrison town of Rawalpindi.