U.S. Marine airstrikes targeting insurgents sheltering in Iraqi residential neighborhoods are killing civilians as well as guerrillas along the Euphrates River in far western Iraq, according to Iraqi townspeople and officials and the U.S. military.

Just how many civilians have been killed is strongly disputed by the Marines and, some critics say, too little investigated. But townspeople, tribal leaders, medical workers and accounts from witnesses at the sites of clashes, at hospitals and at graveyards indicated that scores of noncombatants were killed last month in fighting, including airstrikes, in the opening stages of a 17-day U.S.-Iraqi offensive in Anbar province.

"These people died silently, complaining to God of a guilt they did not commit," Zahid Mohammed Rawi, a physician, said in the town of Husaybah. Rawi said that roughly one week into Operation Steel Curtain, which began on Nov. 5, medical workers had recorded 97 civilians killed. At least 38 insurgents were also killed in the offensive's early days, Rawi said.

In a Husaybah school converted to a makeshift hospital, Rawi, four other doctors and a nurse treated wounded Iraqis in the opening days of the offensive, examining bloodied children as anxious fathers soothed them and held them down.

"I dare any organization, committee or the American Army to deny these numbers," Rawi said.

U.S. Marines in Anbar say they take pains to spare innocent lives and almost invariably question civilian accounts from the battleground communities. They say that townspeople who either support the insurgents or are intimidated by them are manipulating the number of noncombatant deaths for propaganda -- a charge that some Iraqis acknowledge is true of some residents and medical workers in Anbar province.

"I wholeheartedly believe the vast majority of civilians are killed by the insurgency," particularly by improvised bombs, said Col. Michael Denning, the top air officer for the 2nd Marine Division, which is leading the fight against insurgents in Anbar province.

In an interview at a Marine base at Ramadi, Anbar's provincial capital, Denning acknowledged that a city was "a very, very difficult place to fight." He said, however, that "insurgents will kill civilians and try to blame it on us."

But some military analysts say the U.S. military must do more to track the civilian toll from its airstrikes. Sarah Sewall, deputy assistant secretary of defense from 1993 to 1996 and now program director for the Carr Center for Human Rights Policy at Harvard, said the military's resistance to acknowledging and analyzing so-called collateral damage remained one of the most serious failures of the U.S. air and ground war in Iraq.

"It's almost impossible to fight a war in which engagements occur in urban areas [and] to avoid civilian casualties," Sewall, whose center is a branch of Harvard's Kennedy School of Government that focuses on issues such as genocide, failed states and military intervention, said in a telephone interview.

"In a conflict like Iraq, where civilian perceptions are as important as the number of weapons caches destroyed, assessing the civilian harm must become a part of the battle damage assessment process if you're going to fight a smart war," she said.

The number of airstrikes carried out each month by U.S. aircraft rose almost fivefold this year, from roughly 25 in January to 120 in November, according to a tally provided by the military. Accounts by residents, officials and witnesses in Anbar and the Marines themselves make clear that Iraqi civilians are frequently caught in the attacks.

On Nov. 7, the third day of the offensive, witnesses watched from the roof of a public building in Husaybah as U.S. warplanes struck homes in the town's Kamaliyat neighborhood. After fires ignited by the fighting had died down, witnesses observed residents removing the bodies of what neighbors said was a family -- mother, father, 14-year-old girl, 11-year-old boy and 5-year-old boy -- from the rubble of one house.

Survivors said insurgents had been firing mortars from yards in the neighborhood just before the airstrikes. Residents pleaded with the guerrillas to leave for fear of drawing attacks on the families, they said, but were told by the fighters that they had no other space from which to attack.

Near the town of Qaim one day last month, a man who identified himself only as Abdul Aziz said a separate U.S. airstrike killed his grown daughter, Aesha. Four armed men were also found in the rubble of her house, he said.

"I don't blame the Americans. I blame Zarqawi and his group, who were using my daughter's house as a shelter," said Abdul Aziz, referring to Abu Musab Zarqawi, leader of the foreign-dominated group al Qaeda in Iraq.

Abdul Aziz spoke beside his daughter's newly dug grave, in a cemetery established for the 80 to 90 civilians who Anbar officials said were killed in the first weeks of the offensive. Several dozen new graves were evident, and residents said more than 40 victims of the fighting were to be buried that day alone. Witnesses saw only 11, all wrapped in blankets for burial. Residents said two of the 11 were women.

Abdul Aziz's grandsons ascribed blame for their mother's death more pointedly. "She was killed in the bombing by the Americans," said Ali, 9, the oldest of three brothers.

Operation Steel Curtain is representative of a series of offensives in western Anbar that began in late April. Brig. Gen. James L. Williams of the 2nd Marine Division described them as a town-by-town campaign to drive out insurgents and establish a permanent Iraqi army presence in the heavily Sunni Arab region. Iraqi and foreign insurgents use the Euphrates River communities for bases and for logistics support to funnel money, recruits and ordnance from Anbar and neighboring Syria to fighters planning attacks elsewhere in Iraq.

Steel Curtain involved 2,500 U.S. Marines, soldiers and sailors and about 1,000 soldiers of the U.S.-trained Iraqi army, including newly established units of locally recruited scouts commissioned mainly for their knowledge of the area, the Marines said. As the Iraqi and U.S. forces moved through Husaybah, Karabilah and other towns, Marines said, they encountered scores of mines and insurgent-rigged bombs made from artillery shells or other ordnance. Ten Marines and 139 insurgents died in the offensive, the Marines said. They gave no totals for known civilian deaths.

Statements issued by the U.S. military during the offensive reported at least two incidents that were described as airstrikes unwittingly conducted on buildings where civilians were later found to have been present.

On Nov. 8, a man in Husaybah led U.S. and Iraqi forces to a house destroyed by U.S. airstrikes the previous day, Marines said. Searching the rubble, Iraqi troops and U.S. Marines found two wounded civilians -- a young girl and a man -- and recovered five bodies.

The Marines were told that fighters loyal to Zarqawi had forced their way into the house, killed two of the people inside and locked the rest of the family on a lower floor before using the building to attack Iraqi and U.S. forces clearing the neighborhood.

"The soldiers and Marines had no knowledge of the civilians being held hostage in the home at the time of the attack," Marines said in a statement. It could not be determined if that airstrike was the same as the one described by witnesses who watched removal of the dead family.

On Nov. 15, U.S.-led forces called in an airstrike after coming under small-arms fire from a building in the hamlet of New Ubaydi. Two men ran from the building waving white flags after the airstrike, followed by 15 male and female civilians, a U.S. Marine statement said.

Marines described other instances of insurgents hiding among civilians in Anbar, including occasions when they dressed as women and tried to pass unnoticed among townspeople fleeing the battles. Residents, local officials and emergency workers said insurgents often sheltered among civilians in urban neighborhoods.

Arkan Isawi, an elder in Husaybah, said he and four other tribal leaders gathered to assess the damage while the operation was still underway and identified at least 80 dead, including women and children. "I personally pulled out a family of three children and parents," he said.

An exact count, however, was impossible, he said. "Anyone who gives you a number is lying, because the city was a mess, and people buried bodies in backyards and parking lots," with other bodies still under rubble, Isawi said.

Townspeople, medical workers and officials often exaggerate death tolls, either for effect or under orders from insurgents. However, accounts from other officials and residents are borne out at least partially by direct observation of bodies and other evidence.

The accounts of U.S. Marines and Iraqi civilians of airstrikes often diverge sharply.

On Oct. 16, for instance, a U.S. F-15 pilot caught a group of Ramadi-area insurgents planting explosives in a blast crater on a road used by U.S. forces, Denning said. The F-15 dropped a bomb on the group, and analysis of video footage shot by the plane showed only what appeared to be grown men where the bomb struck, Denning said. After the airstrike, he said, roadside bombs in the area "shut down to almost nothing.

"That was a good strike, and we got some people who were killing a lot of people," Denning said.

Capt. Jeffrey S. Pool, a spokesman for the 2nd Marines, said it was not possible that children were killed in that strike unless they were outside the range of the F-15's camera.

Residents, however, said the strike killed civilians as well as insurgents, including 18 children. Afterward, at a traditional communal funeral, black banners bore the names of the dead, and grieving parents gave names, ages and detailed descriptions of the children they said had been killed, witnesses said. The bodies of three children and a woman lay unclaimed outside a hospital after the day's fighting.

American commanders insist they do everything possible to avoid civilian casualties, but overall, Denning said, "I think it would be very difficult to prosecute this insurgency" without airstrikes.

The precision-guided munitions used in all airstrikes in Anbar "have miss rates smaller than the size of this table," Denning said in the bare-bones cafeteria of one of several Marine bases around Ramadi. He said that officers at Ramadi and at the Marines' "lessons learned" center in Quantico coordinate each attack using the best intelligence available. "I have to sell it to about two or three different chains of command: 'What are you doing to make sure there are no civilian casualties?' " Denning said.

Sewall, the former Pentagon official, also said air power often is the best means for taking out a target more cleanly than ground forces could. But, she said, U.S. forces don't do enough after the airstrikes to figure out whether each one succeeded in hitting the intended targets while sparing civilians.

Marine officers said their lessons-learned center at Quantico did not try to assess civilian casualties from attacks. At the Pentagon, routine bomb-damage assessments rely heavily on the examination of aerial photos and satellite images, which Sewall said were "good for seeing if a building was hit, but not as good for determining who was inside."

"I have enormous respect for the extent to which U.S. air power has become discriminate," Sewall said. "But when you're using force in an urban area or using force in an area with limited intelligence," and facing an enemy actively "exploiting distinctions between combatants and noncombatants, air power becomes challenging no matter how discriminate it is.

"When it comes to the extent to which they are minimizing civilian harm, the question becomes: How do you know?" Sewall said.

Staff writer Thomas E. Ricks in Washington contributed to this report.