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."
"When we shoot into a compound, that should only be for the protection of our forces," he said. "I want everyone to understand that."
The statements by General McChrystal signaled the latest tightening of the rules for using airstrikes, which, while considered indispensable for protecting troops, have killed hundreds of civilians.
They have also angered the Afghan government, which has repeatedly criticized American and NATO forces for not taking enough care with civilian lives.
In December, the American commander at the time, Gen. David D. McKiernan, issued guidelines ordering his soldiers to use force that was proportional to the provocation and that minimized the risk of civilian casualties.
General McChrystal's new guidelines follow a deadly episode last month in the Afghan village of Granai, where American airstrikes killed dozens of civilians.
The episode highlighted the difficulties facing American officers under fire, as they are forced to balance using lethal force to protect their troops with rules restricting the use of firepower to prevent civilian deaths.
The episode, on May 4, began when a large group of Taliban fighters attacked a group of about 200 Afghan soldiers and police officers and American advisers. During the firefight, which began just after noon and carried on into the night, the Americans on the ground called for air support.
American fighter jets, and then bombers, came to the scene, dropping a number of 500- and 2,000-pound bombs. The bombs succeeded in ending the attack, but they did much more damage as well.
A Pentagon report estimated that at least 26 civilians had been killed in the airstrikes. It concluded that American personnel had made significant errors, including violating procedures, that led to those deaths. Among those errors, the report said, was a failure by the American personnel to discern whether Afghan civilians were in the compound before they attacked.
Other credible estimates of civilian deaths in Granai ranged much higher. An investigation by a Kabul-based group, the Afghan Independent Human Rights Commission, said that at least 86 women and children had been killed, and as many as 97 civilians altogether. The Afghan government said 140 civilians had been killed.
The Pentagon report did not dispute the conclusions reached by the Afghan Independent Human Rights Commission, and referred to its "balanced, thorough investigation."
The deaths in Granai make up part of the huge rise in civilian casualties that are characterizing the war in Afghanistan.
A United Nations report found that the number of Afghan civilians killed in 2008 was 40 percent higher than in 2007. The Taliban and other insurgents caused the majority of the civilian deaths, primarily through suicide bombers and roadside bombs.
The changes highlighted by General McChrystal go to the heart of what went wrong in Granai. In that case, there were at least four airstrikes: the first by F-18 fighters and the other three by a B-1B bomber. The report found that it was the last two airstrikes that probably caused the civilian deaths.
In those cases, the report found, the bomber's crew tracked suspected Taliban fighters as they entered a building, and then attacked without determining whether civilians were inside. The report said there were probably civilians inside those buildings when they were destroyed.
Under the rules that General McChrystal outlined, those strikes would almost certainly be prohibited. They would be prohibited, the general said, even if it meant letting some Taliban get away.
Referring to airstrikes, General McChrystal said, "If it is just to defeat the enemy, then we are not going to do it, even if it means we are going to step away from that firefight and fight another time."
According to the Pentagon report, the B-1B dropped five 500-pound bombs and two 2,000-pound bombs. The initial airstrikes, carried out by four F-18 fighters-bombers, the report said, killed insurgents but no civilians.
Ahmad Nader Nadery, the director of the Afghan Independent Human Rights Commission, said Sunday that the American response in Granai was "disproportionate." And he said he was pleased by the changes outlined by General McChrystal.
"We are looking forward to seeing the new guidelines, and actually seeing how they would be translated into practice," he said.
Last September, Defense Secretary Robert M. Gates ordered new rules specifically to defuse tensions over Afghan civilian deaths.
During a recent visit to Kabul, Mr. Gates said the American military would quickly apologize and offer compensation to survivors in cases of civilian deaths, even in advance of formal investigations to determine exactly what had happened.
"I think the key for us is, on those rare occasions when we do make a mistake, when there is an error, to apologize quickly, to compensate the victims quickly, and then carry out the investigation," Mr. Gates said after a meeting with President Hamid Karzai.
Thom Shanker contributed reporting from Washington.