WASHINGTON - The senior American commander in Afghanistan says the ability to train and advise the still inexperienced Afghan security forces will be constrained if the U.S. troop level is cut to 5,500, as President Barack Obama has proposed.

Army Gen. John F. Campbell tells the Senate Armed Services Committee on that "very little" training will be done with fewer American forces.

Campbell is sparring with the committee chairman, Republican Sen. John McCain of Arizona, over the wisdom of the troop reductions.

McCain wants to know whether the 5,500 U.S. troops are adequate to perform the training mission as well as counterterrorism operations.

Campbell says much will depend on how quickly the Afghan forces improve.

Campbell says he's preparing to go down to 5,500 "as I am ordered."