With the end of this year’s fighting season, the Taliban have weathered the biggest push the American-led coalition is going to make against them. A third of all American forces left by this month, and more of the 68,000 remaining may leave next year, with the goal that only a residual force of trainers and special operations troops will remain by the end of 2014.

Bringing Pakistan into the search for Taliban contacts is also an uncertain strategy, American officials said. The details of the new vetting committee have yet to be worked out, and “if we are depending on Pakistan, it comes with an asterisk,” one of the officials said. “We never know whether they will see it through.”

The American shift toward a more peripheral role in peace efforts represents another retreat from Washington’s once broad designs for Afghanistan, where the surge, along with a sharp escalation of nighttime raids by Special Operations Forces against Taliban field commanders, were partly aimed at forcing the Taliban into negotiations, making a Western withdrawal more feasible.

For a brief moment, the strategy appeared to be working: preliminary talks, painstakingly set up throughout 2011, opened early this year in Qatar, in the Persian Gulf.

The effort fell apart when the Obama administration, faced with bipartisan opposition in Washington, could not make good on a proposed prisoner swap, in which five Taliban leaders held at Guantánamo Bay, Cuba, would have been exchanged for the sole American soldier held by the insurgents, Sgt. Bowe Bergdahl.

The trade was to be an initial confidence-building measure that would lead to more serious talks. If it is revived by the Obama administration, it would come after the presidential election, most likely leaving too little time to reach a deal before 2014, some current and former American officials said.

In Washington, “the tone of the whole discussion has shifted to a less U.S.-led approach and toward a more Afghan-led approach, but one that will be over a longer term,” said Shamila N. Chaudhary, a South Asia analyst at the Eurasia Group who served as the director for Pakistan and Afghanistan at the National Security Council.