WASHINGTON  The Pakistani Army’s announcement last week that it planned no new offensive against militants for as long as a year has deeply frustrated senior American military officers, and chipped away at one of the cornerstones of President Obama’s strategy to reverse the Taliban’s gains in Afghanistan and Pakistan.

When Mr. Obama announced his decision in December to send 30,000 additional troops to Afghanistan, he and his aides made clear that the chances of success hinged significantly on Pakistan’s willingness to eliminate militants’ havens in its territory, including in the tribal region of North Waziristan. United States officials described the American and NATO surge of troops as a hammer, but they said it required a Pakistani anvil on the other side of the border to prevent the Taliban from retreating to the mountains.

Now that strategy appears imperiled by Pakistan’s latest statement. On Thursday, soon after Defense Secretary Robert M. Gates arrived on a two-day trip to the country, the Pakistani Army’s chief spokesman, Maj. Gen. Athar Abbas, rebuffed American pressure to step up attacks in North Waziristan. That area is the main base of operations for the Haqqani network, which stages operations against American and Afghan forces in Afghanistan. It is believed to be responsible for many of the attacks on Kabul, including a devastating assault early last week near the presidential palace.

Fighters from Al Qaeda and the Pakistani Taliban have also been concentrated in North Waziristan, including many who were driven out of their positions in South Waziristan by recent Pakistani Army operations.