But even as the Americans pledge revenge against the Haqqanis, and even amid a new debate in the Obama administration about how to blunt the group’s power, there is a growing belief that it could be too late. To many frustrated officials, they represent a missed opportunity with haunting consequences. Responsible for hundreds of American deaths, the Haqqanis probably will outlast the United States troops in Afghanistan and command large swaths of territory there once the shooting stops.

American military officers, who have spent years urging Washington to take action against the Haqqanis, express anger that the Obama administration has still not put the group on the State Department’s list of terrorist organizations out of concern that such a move would scuttle any chances that the group might make peace with Afghanistan’s government.

“Whoever is in power in Kabul will have to make a deal with the Haqqanis,” said Marc Sageman, a former C.I.A. officer who served in Pakistan during the Soviet-Afghan war. “It won’t be us. We’re going to leave, and those guys know it.”

When their threat was less urgent, the Haqqanis — estimated at 5,000 to 15,000 fighters in the mountains of Afghanistan and Pakistan — were not a top priority for the Americans. But even then the United States also had little leverage against them. The Haqqanis have expanded their reach and numbers as top American officials have tried repeatedly over the last decade to berate and cajole officials in Pakistan to cut ties to a group it considers essential for its own security, all with little effect.