KABUL, Afghanistan  The new American commander in Afghanistan said he would sharply restrict the use of airstrikes here, in an effort to reduce the civilian deaths that he said were undermining the American-led mission.

In interviews over the past few days, the commander, Gen. Stanley A. McChrystal, said the use of airstrikes during firefights would in most cases be allowed only to prevent American and other coalition troops from being overrun.

Even in the cases of active firefights with Taliban forces, he said, airstrikes will be limited if the combat is taking place in populated areas  the very circumstances in which most Afghan civilian deaths have occurred. The restrictions will be especially tight in attacking houses and compounds where insurgents are believed to have taken cover.

“Air power contains the seeds of our own destruction if we do not use it responsibly,” General McChrystal told a group of his senior officers during a video conference last week. “We can lose this fight.”