The combat troops from the 3rd Infantry Division's 2nd Brigade arrived to take over the area from the 3rd Armored Cavalry Regiment. Two battalion-sized task forces took up positions around the city of Fallujah, 30 miles west of Baghdad; another task force took over two military airfields in Habaniyah, five miles farther west. 

Two major highways connecting Baghdad to Syria and Jordan run through the two cities, where about 300 soldiers from the 3rd Armored Cavalry Regiment have maintained a mostly symbolic presence. 

But after violent demonstrations and several attacks on U.S. troops, commanders decided to send in the battle-tested 2nd Brigade, which captured most of Baghdad during the war. 

In addition to patrolling the area, the brigade will also work with local leaders on community service projects at schools and hospitals to improve relations with residents. 

Lt. Gen. David McKiernan, commander of American ground forces in Iraq, said he doubted the attackers were coordinating their efforts. 

"These are localized, decentralized attacks by those who were part of the old regime. I don't see a national effort across Iraq," McKiernan said Wednesday. "I don't see any pattern of centralized command and control over these incidents." 

He said the spate of attacks signifies a last-ditch effort by Saddam's supporters - not a gathering resistance movement. 

"I see it as the completion of the removal of Saddam Hussein's regime," McKiernan said at a news conference in Baghdad. "They don't want a democratic Iraq to succeed because they don't have a role in it." 

In Fallujah and the neighboring cities of Ramadi and Habaniyah, the streets were quiet Wednesday as soldiers from the 3rd Infantry Division went on patrol. Residents went about their business, passing American forces without incident. 

The road between Baghdad and Fallujah was crowded with U.S. Army trucks moving west. 

Anger in Fallujah grew in late April, when confrontations between residents and American forces left 18 Iraqis dead and at least 78 wounded. Residents accuse U.S. troops of using excessive force and of not respecting Islamic practices. 

As troops moved into Fallujah, other American infantrymen immediately began setting up shop at Habaniyah Air Base, built by the British in the early 1950s. 

Habaniyah grew up around the air base, where abandoned Soviet fighter jets and cargo planes still sit on the runway, slowly deteriorating. Uniforms left at the base have the insignia of Republican Guard troops, and hundreds of gas masks litter the barracks. 

An Iraqi special forces base was located northeast of Fallujah, and many military-age men in the cities, some in very good physical condition, have scowled or made obscene gestures toward U.S. troops. 

"You can tell who used to be in the military," said Capt. Chris Carter, commander of A Company, 3rd Battalion, 7th Infantry Regiment, which is occupying the air base. 

At dawn Wednesday, the 2nd Brigade loaded 88 Abrams tanks and 44 Bradley Fighting Vehicles onto cargo trucks and dropped them off outside the two cities. The soldiers then drove the combat vehicles to their new positions and began establishing their bases. 

There wasn't much to work with. 

Most of the buildings had been looted after Iraqi troops abandoned the base, with almost everything that could be removed - including light switches and door frames - stolen. 

The troops were greeted by curious shepherds, grazing sheep and goats on the base grounds. The soldiers began cleaning the old tin-roofed barracks to use themselves. 

"It won't be that bad, once we get some fans blowing through here," Carter said, looking around the shell of one building, where even the tiles on the fireplace had been pried off by looters. 

"It's like a really bad summer camp," 1st Lt. Eric Hooper, Carter's second in command, said as he set up a mosquito net over his cot.