Petraeus has not commented publicly on the need for more troops, but a U.S. defense official and a senior NATO official directly familiar with his thinking and the entire matter have confirmed details to CNN.

The Petraeus proposal for more troops has been briefed to NATO officials behind closed doors.

According to the NATO source, it calls for an additional 2,000 troops including at least 750 personnel to serve as trainers for Afghan forces. The trainers specifically would work to teach Afghan units how to support their operations in the field. The balance of the forces would work largely to counter the still significant threat posed by improvised explosive devices (IEDs).

Another NATO official tells CNN "it's highly likely" many of the additional forces will be U.S. troops. Some NATO member countries are politically ambivalent about the war, he noted. And practically, it is only U.S. forces that have the most advanced equipment to counter roadside bombs

In May, Defense Secretary Robert Gates sent 850 U.S. military trainers on a temporary deployment when European countries could not pledge enough of their own forces. This latest need for 2,OOO forces goes beyond that to include counter-IED forces, although some small number of the at least 750 additional trainers could replace those already there.

No final decisions have been made on any additional U.S. troops.

NATO military authorities are scheduled to meet in the coming days to try to get specific troop commitments from member nations. The goal is to get the matter resolved before a November NATO summit in which U.S. and NATO military commanders are expected to discuss progress in the war.

The potential for yet another troop increase, even a relatively small one, is already being defended by NATO. The senior official told CNN "this relatively small uplift -- less than 2 percent of the 150,000 in theatre from the coalition -- reflects the direction of the campaign: training the Afghan security forces to prepare for transition, as well as protecting our forces."

A U.S. military official also confirms that in recent weeks the discussion of the "withdrawal" of forces from certain areas of Afghanistan beginning in July 2011 has taken a bit of a twist.

The official said the withdrawal in some areas will signify that those areas may be turned over to Afghan control, but that may not mean troops will come home. The latest options call for taking those troops not needed and sending them to other areas where security is still poor.