WASHINGTON, Feb. 17 — The commander of American-led forces in Afghanistan said Tuesday that the military had adopted new tactics to combat Taliban and Al Qaeda militants in the country. The officer, Lt. Gen. David W. Barno of the Army, said that in the past three months, American units down to the level of 40-soldier platoons had been dispatched to live in villages where they can forge ties with tribal elders and glean better information about the location and activities of guerrillas. In the past, he said, American forces typically gathered intelligence about hostile forces, carried out focused raids for...