BAGHDAD — U.S. forces firing from helicopters pursued armed militants loyal to a radical anti-American Shiite cleric into a western Baghdad slum yesterday, killing at least 18 people, reportedly including some civilians.

Meanwhile, as a counterinsurgency campaign continues to target suspected sanctuaries of gunmen and bomb-builders, a senior U.S. commander in Iraq dismissed calls to reduce the number of troops, saying it would be a "giant step backwards." Maj. Gen. Rick Lynch, who commands more than a third of the 30,000 additional troops deployed to Iraq in recent months, disputed a call from a prominent Republican senator for Bush to begin reducing troops.

U.S.-led forces said the predawn raid yesterday on the capital's Shula district was in response to an insurgent attack on a U.S. patrol in the area. But residents said the U.S. helicopter attack caught many in the Shiite community controlled by Muqtada al-Sadr's Al Mahdi Army asleep on their roofs, where they go to escape the stifling heat of apartments that get only an hour or two of electricity each day.

Hospital officials reported two women's bodies among those brought to two area morgues, and an al-Sadr spokesman said four women were among the dead. Angry relatives and neighbors of the killed and injured vowed retribution as they carried the victims' coffins through the teeming streets.

Al-Sadr, whom U.S. military leaders accuse of directing death squads and a campaign of harassment against U.S. troops in Iraq, denounced the air attacks and called on supporters to stage protests across the country.

A U.S. soldier died in combat near Samarra, the U.S. military announced. The death brought to 3,725 the number of American soldiers killed in Iraq since the war began 4 1/2 years ago, according to www.icasualties.org.

Gen. Peter Pace, chairman of the Joint Chiefs of Staff, is expected to recommend reducing the current 160,000 U.S. deployment by almost half, officials in Washington told the Los Angeles Times.

Pace released a statement yesterday saying that the Joint Chiefs and he were reviewing a range of options and that he would give his advice to Bush in private. "The L.A. Times article is purely speculative," Pace said. "I take very seriously my duty to provide the best military advice to the president." On Thursday, influential Virginia Republican Sen. John W. Warner, a former Navy secretary, also called for a reduction.

Lynch, who commands U.S. troops from southern Baghdad to the Saudi border, made clear in a video linkup with Pentagon reporters he opposes a drawdown.

"In my battle space, if soldiers were to leave ... having fought hard for that terrain, having denied the enemy their sanctuaries, what would happen is the enemy would come back," Lynch said. "He'd start building the bombs again. He'd start attacking the locals again. He'd start exporting that violence to Baghdad. We would take a giant step backwards."