WASHINGTON - Stricter new rules for combat and bombing raids in Afghanistan - to be announced soon by the U.S. military - may well complicate the battlefield for American forces, but officials said the changes were crucial to reducing civilian deaths, which have been undermining the war effort.

Analysts said they did not expect the new guidelines to immediately translate to more peril for ground troops that depend on air support in battle, but they said that if some combat encounters under the new rules lead to more dangers, the risk is worth the effort if it builds more Afghan support for the war.

"We are not in Afghanistan to make sure that fewer Americans die," said Andrew Exum of the Washington think tank Center for a New American Security. "We are in Afghanistan to make sure fewer Afghan civilians die."

Gen. Stanley McChrystal, who took command of the eight-year-old war in Afghanistan last week, is expected soon to give U.S. and NATO forces new guidelines on air strikes, telling them to break away from fights with enemy forces hiding in Afghan houses when they can.

McChrystal will issue orders within days, saying troops may attack insurgents hiding in houses only if the U.S. or NATO forces are in imminent danger and must return fire, a U.S. military spokesman, Rear Adm. Greg Smith, said yesterday.

"But if there is a compound they're taking fire from, and they can remove themselves from the area safely, without any undue danger to the forces, then that's the option they should take," Smith said. "Because in these compounds we know there are often civilians kept captive by the Taliban."

Although guidelines have been tightened before, the order would be one of the strongest measures taken by a U.S. commander to protect the Afghan population.

Commanders and top Defense Department officials alike say civilian deaths hurt their counterinsurgency mission because they turn average Afghans against the government and U.S. and NATO forces.

The change probably will encourage Taliban and other insurgents to continue, or even increase, the practice of hiding among civilians and using them as human shields, Exum acknowledged. "But if they do that, then they're going to lose the support of the population," he said.

Exum said the guidelines likely would also result in fewer air strikes.

Lawrence Korb of the Washington think tank Center for American Progress, agreed, noting that there was a huge caveat in the new guidelines that should provide protection for the ground forces - "if you're in danger, you need to return fire."

"The question is not winning the battle," he said. "It's winning the war."

Civilian casualties are a major source of friction between Afghan President Hamid Karzai and the United States. NATO, U.S., and Afghan forces killed 829 civilians last year, according to the United Nations.

In the most recent instance, a May 4-5 battle between U.S. and Afghan forces and militants in western Farah province killed dozens of civilians. A U.S. report last week said U.S. forces killed an estimated 26 civilians. Karzai's government said 140 were killed, while an Afghan human-rights group said the number was about 100.

Military forces had not made absolutely certain that civilians were not present, officials concluded.