The townspeople were in the middle of an impromptu celebration, cheering and clapping and whistling for the American soldiers who only hours before had marched through the center of this holy city. Then the shots rang out.

"Small-arms fire! Get your heads down!" Lt. Col. Marcus DeOlivera shouted to his soldiers. "Watch those rooftops!"

The Army convoy jerked to a halt along the main road of Najaf. People fled the sidewalks. A man was so startled he fell off his bicycle. The 50 or so infantry riflemen of the 101st Airborne Division took cover behind their Humvees and scanned the rooftops through their weapons' sights.

A blue car sped from behind a building. Two Iraqis leaned out the front windows, pointing Kalashnikov rifles toward the convoy.

"He's coming for us!" DeOlivera screamed. "Take him out! Hit the car! The blue car! Now!"

The soldiers of 1st Battalion of the 327th Infantry Regiment started firing: M-4s, 50-caliber machine guns, a Mark-19 grenade launcher. The bullet-pocked car crashed into a pole, smoking, the men inside dead and slumped atop each other.

For a moment, the city fell quiet. But soon came U.S. attack helicopters and the Hellfire missiles and the explosions that shook the ground as the Army destroyed the area from which the car had come. It was a suspected weapons cache.

Then the convoy rolled on, and the people returned to the sidewalks, smiling and giving the soldiers the thumbs-up sign.

The violent flurry Wednesday afternoon culminated a dramatic day in the historic, central Iraq city of Najaf. After three days of biting around the edges of the city--storming and capturing a university, several military compounds and a factory--the 101st Airborne made a show of force just after dawn, marching for more than 5 unopposed miles through the city center with more than 130 heavily armed soldiers.

Still, for all the symbolism of having soldiers walk through the center of an Iraqi city and even being warmly welcomed along the route, the convoy ambush later in the day revealed how committed some of Saddam Hussein's most loyal fighters are and how fragile the control of the volatile nation really is.

Late Wednesday, despite three days of almost constant aerial bombings of suspected militia strongholds and weapons storage facilities, paramilitary elements remained firmly rooted in Najaf while elements of the 101st Airborne continued to search for them. During a raid on a building from which snipers had been firing, soldiers found detailed maps of troop locations throughout the city and the kind of technology that many had believed the Iraqis did not possess, including night-vision goggles.

"Would I say that we now have the city firmly in hand?" DeOlivera asked. "No, I don't think I would go that far. But I would say it's certainly more in hand today than it was yesterday. And today has been one hell of a day."

The mission assigned to Alpha Company on Wednesday morning was simple: About 130 men--the company plus a scout team and a sniper team--would walk nearly 6 miles through town to show the residents of Najaf that America was there. No one used the word "liberate," but that was clearly the mood.

"It's pretty cool when you know people are happy to see you," said Staff Sgt. Scott Miller. "It makes you feel like you are doing what you are supposed to be doing."

Carrying anti-tank missiles and grenade launchers, the soldiers set out in two long lines, one on either side of the four-lane road that cuts through Najaf.

Townspeople awed at first

The soldiers passed Noor Al Husaeen Hotel and Ain Ali Restaurant and Dar Al Auda Guesthouse. They passed women carrying cartons of eggs and children who imitated the American military salute. They passed blown-out buildings and bombed-out cars and local men walking with their hands in the air to show they had no gun.

Two attack helicopters flew low over the soldiers.

A Humvee broadcast a constant message in Arabic over loudspeakers. "Entebah, entebah, entebah," it began, "Attention, attention, attention." The message then went on to tell people that the U.S. military meant them no harm.