Kabul, Afghanistan ? Crouched in a field of opium poppies, a young Marine lieutenant pleaded over the radio for an airstrike on a compound where he believed a sniper was firing at his troops. Request denied. Civilians might be inside and the Marines couldn’t see a muzzle flash to be absolutely sure the gunman was there.

President Barack Obama, accompanied Wednesday by Gen. David Petraeus, announces at the White House in Washington that Petraeus would replace Gen. Stanley A. McChrystal, the commander of Western forces in Afghanistan.

The lieutenant’s frustration, witnessed by an Associated Press journalist in February in Marjah in southern Afghanistan, points to a Catch-22 dilemma facing the NATO force: how to protect troops against an enemy that lives — and fights — among the population without killing civilians and turning the people against the U.S.-led mission.

Those complaints from the ranks are among the issues facing Gen. David Petraeus — along with relations with a weak Afghan government and jittery allies; slow and uncertain progress on the battlefield; and frayed ties to the civilian side of the mission.

But among the most sensitive and important to the troops he commands and to supporters of the military at home will be whether to continue the rules laid down by his predecessor, Gen. Stanley McChrystal, that stress saving civilian lives but sometimes leave U.S. forces at greater risk.

Those rules, issued a year ago, helped make McChrystal a hero among many Afghans because they brought down the number of civilian casualties blamed on the NATO-led force. The rules were issued at a time of a rising tide of public anger over Afghan civilians killed by mistake in airstrikes and by heavy weapons such as cannons and mortars.

Down in the ranks, however, the rules are widely perceived as too restrictive, playing into the hands of the Taliban who appear keenly aware of the regulations. Some troops believe the rules cost American lives and force them to give up the advantage of overwhelming firepower to a foe who shoots and melts back into the civilian population.

At a Pentagon news conference Thursday, Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, hinted about possible changes in the rules when asked about troops who feel “they’re being asked to fight with one hand tied behind their back.”

“Any new commander, Gen. Petraeus included, will go in, assess his command, and what it is going to take to achieve the mission,” Mullen said, adding that the general “certainly has the flexibility to make changes that he thinks are necessary.”

But Mullen also said that doesn’t “portend changes” in the rules. He noted that Petraeus, who was McChrystal’s boss, is “very aware of the tactical directive” and was involved in approving it as commander of the U.S. Central Command, which is responsible for the wars in Afghanistan and Iraq.

The counterinsurgency strategy, which the military calls COIN, is based on protecting civilians and weaning them away from the insurgents.

According to a U.N. report, at least 2,412 civilians were killed last year — a 14 percent increase over 2008. But the percentage of those deaths caused by international and Afghan government forces dropped from 39 percent in 2008 to 25 percent last year, the U.N. said.

The U.N. attributed much of that decrease to the directive issued by McChrystal, who was dismissed this week for disparaging remarks that he and his aides made about senior members of the Obama administration to Rolling Stone magazine.

“Winning hearts and minds in (counterinsurgency warfare) is a coldblooded thing,” McChrystal who was quoted in the article as telling an American soldier who expressed frustration about the rules. Trying to convince him, McChrystal said: “The Russians killed 1 million Afghans, and that didn’t work.”