One question is the scope of the mission for the American counterterrorism force. The targets of the counterterrorism force would include Al Qaeda and possibly Lashkar-e-Taiba, the Pakistan-based militant group linked to Al Qaeda that was responsible for the 2008 Mumbai attacks, and which is found in small numbers in northeast Afghanistan. The Islamic Movement of Uzbekistan might also make the list.

But it was unclear whether the Pakistani-based Haqqani network, which American commandos have focused on for the past two years, would also be a potential target of the American force. Officials say that does not appear to be contemplated by the White House.

An important question for the NATO mission after 2014 is what level of the Afghan military hierarchy they would advise. It is generally expected that they would advise seven regional Afghan Army corps and several regional Afghan police headquarters. The arrangement would largely insulate the NATO advisers from the battlefield, though officials said advisers might accompany Afghan brigades on major operations.

It is unlikely that NATO officers would advise Afghan battalions on the battlefield. That would require many more advisers than the alliance is likely to muster and would entail more risk than most nations seem prepared to assume, though some American experts believe it would make the Afghan military more effective. Still, NATO special operations advisers would be likely to accompany Afghan Army commandos and police SWAT-type units on the battlefield, under the emerging plan.

A major challenge is that Afghanistan will not have an effective air force before 2017, if then. American officials said that NATO airpower would remain in Afghanistan after 2014 but will likely only be used on behalf of NATO and American troops and perhaps Afghan units that are accompanied by NATO advisers. NATO forces rely heavily on airpower for airstrikes, supply and medical evacuation since Afghanistan’s roads are poor and often seeded with bombs.

To compensate for Afghanistan’s limited airpower, American officials are working on a number of fixes, including providing Afghan forces with armored vehicles that would be equipped with mortars and assault guns. The United States is also looking into expanding the purchase of turboprop planes for the Afghans and is trying to help Afghan pilots learn to fly at night.

Equally troubling is the problem of medical evacuations. After 2014, the Afghans will almost certainly need to rely on a system that depends more on ground transportation than helicopters. The Americans want to help them develop more field hospitals.