KABUL, Afghanistan (AP) – Defense Secretary Robert Gates offered the people of Afghanistan his “personal regrets” Wednesday for U.S. airstrikes that have killed civilians and said he would try to improve the accuracy of air warfare, the imperfect fallback for U.S. commanders who say they don’t have enough ground forces for the deepening Afghanistan war.

“As I told them, I offer all Afghans my sincere condolences and personal regrets for the recent loss of innocent life as a result of coalition airstrikes,” Gates said after meeting with Afghan President Hamid Karzai. “While no military has ever done more to prevent civilian casualties, it is clear that we have to work even harder.”

Gates’ unusual apology followed a frank assessment from the top military commander in Afghanistan: There aren’t enough U.S. ground forces in Afghanistan, so the military is relying more heavily on air power. Air power runs a greater risk of civilian deaths in a country where insurgents do not wear uniforms and they intentionally mix with the general population.

Gen. David McKiernan, the commander of international forces in Afghanistan, had said earlier that the chronic shortage of U.S. troops in Afghanistan is forcing commanders to rely more on air combat. U.S. airstrikes that kill civilians have angered and embarrassed the U.S.-backed Afghan government, and Karzai has been bitterly critical of such attacks.

Gates agreed to an Afghan proposal to establish a permanent U.S.-Afghan group to investigate all incidents involving civilian casualties. That would be a shift from the current practice of U.S., Afghan and international probes proceeding separately.

And the defense secretary said he favored “a bit of a change of approach” in how U.S. military authorities react when allegations arise over unintended damage from U.S. air attacks.

“I think the key for us is, in 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,” Gates told reporters later at Bagram airfield north of Kabul, where he received a briefing from an Air Force general on the rules and restrictions U.S. pilots must follow when providing aerial support to U.S. and allied troops engaged in ground fighting.

He then made a brief tour of the flightline where an array of jets were parked under a bright sun.

Standing beside a workhorse in the fleet of planes used in so-called close-air support missions – an Air Force A-10 Warthog whose painted nose art featured the gaping jaws of a shark – Gates said Karzai had assured him that the Afghan people “are still very friendly toward the United States.”

Taken together, the Pentagon chief’s pronouncements during his first visit to Afghanistan since December reflected concern in the Bush administration that recurring allegations that U.S. bombs deliberately target civilians – accusations denied by the U.S. – are seriously undermining a central U.S. goal: to persuade ordinary Afghans that the U.S. military is here to protect them and that the enemy U.S. forces are fighting is also their enemy. This “hearts and minds” battle is central to the U.S. counterinsurgency strategy.

This is a problem facing not only the Bush administration but the next U.S. president as well.

There are about 33,000 U.S. troops in Afghanistan, and the Pentagon is sending another Army brigade, numbering about 3,700 soldiers, in January. They will join a fight against a determined insurgency opposed both to Karzai’s government and to the presence of foreign troops.

A roadside blast Wednesday in eastern Afghanistan killed four U.S. coalition soldiers and an Afghan.

U.S. military deaths in Afghanistan in 2008 already have surpassed the record 111 deaths the U.S. suffered here last year. The number of attacks on U.S. forces in eastern Afghanistan has risen by around 30 percent this year compared with 2007, U.S. military officials say.

Of the numerous recent cases of Afghan civilians getting killed in U.S. airstrikes, perhaps the most damaging is the widely publicized attacks of Aug. 22 on a village compound in western Afghanistan. Afghan and U.N. investigators found that up to 90 civilians were killed, including women and children. U.S. investigators first said the civilian toll did not exceed seven, but McKiernan later announced a higher-level U.S. investigation to look into new evidence.

In an interview Tuesday in Kabul, McKiernan said the follow-up U.S. probe should be done in a couple of weeks.

Gates did not comment directly on whether he thought the U.S. had underestimated the toll from the Aug. 22 strikes.

“You have my word,” Gates said, addressing Afghans directly during a news conference, “that we will do everything in our power to find new and better ways to target our common enemies, while protecting the good people of Afghanistan.”