More than 1,000 Marines rolled through this sleepy Tigris River town today and headed for what they expected would be a showdown with a brigade from the Baghdad Division of Iraq's elite Republican Guard.

But the battle was not to be.

By the time the Marines arrived on the scene on the other side of Numaniyah, a week of heavy aerial and artillery bombardment had apparently forced the Iraqi unit to abandon its positions. The Marines faced only sporadic small-arms fire that was quickly suppressed as they moved through town and crossed the Tigris River about 80 miles southeast of Baghdad.

"We expected this to be our heaviest engagement of the war thus far," said Lt. Col. Christopher Conlin, who commands the 1st Battalion, 7th Marine Regiment. "But it appears that even Saddam's best soldiers are crumbling from the inside."

This morning had the appearances of a prelude to battle.

After sleeping in their chemical suits and protective rubber boots -- they had intercepted an Iraqi radio transmission suggesting that chemical weapons could be used -- the Marines were awakened by the staccato of a Marine artillery battalion barrage fired against Republican Guard positions. Over the next half-hour, about 25 volleys of two dozen or more rounds traveled directly overhead as the Marines cheered the vapor trails and resounding impacts that shook the ground a few miles away. Helicopters and fixed-wing warplanes also bombarded the Iraqi positions as the Marines waited to move in.

"Good morning. This is your wake-up call," shouted Staff Sgt. Jerry Pat Moss, of Arlington, Tex., as the first rounds fell.

Commanders speaking to Marines in cloistered circles in the wheat field where they had spent the night warned them not to tolerate any tactics designed to lull them into a false sense of security.

"Make sure if you see any white flags that there are accompanying actions to suggest they are surrendering," said Maj. Dan Healey, 36, of Worcester, Mass., who commands Baker Company. "If they stay behind their weapons, they get pounded. They've tried that before."

With word that their assault was imminent, the Marines began preparations with a determination not seen since they entered Iraq two weeks ago. Nearly every Marine shaved, to ensure that chemical masks would seal tightly to their faces should they be required to don them. Most scrubbed their weapons with steel-bristled toothbrushes to remove built-up sand and dust that could cause them to jam.

They loaded bulletproof, ceramic plates into their flak vests, some for the first time, and moved ammunition boxes stored underneath benches in their Amtrac amphibious assault vehicles to within arm's reach of the hatches where they stand to fire.

1st Sgt. Dave Jobe gave a quick lesson on firing the AT4, a shoulder-fired anti-tank weapon stored in each Amtrac, to a group of Marines who had never used one before, "in case, for some reason, I can't do it," he said.

They assembled in formation in a plowed field behind a large mud home. As they prepared to move out, a family emerged from inside and waved, and a man in a red-and-white checkered head scarf and black robe held a baby up in the air and waved to the columns of armored vehicles.

At about 9 a.m., they entered the town of Numaniyah, which had been under Marine control since Wednesday. The town at first appeared to be deserted, its streets abandoned and bombed-out buildings and shuttered vending stalls unoccupied. But as they turned down a main street, the Marines were greeted by hundreds, if not thousands of Iraqi men, women, and children clapping their hands, waving and giving them a thumbs-up sign.

One young boy in a baseball cap blew kisses with both hands. Four others jumped up and down on a blown tire as the troops passed. The Marines waved back as they proceeded along the Tigris River to a staging area. Many said it was just the sort of welcome they had been waiting for.

"They had told us we would be cheered when we invaded, but we hadn't really seen it until today," said Lance Cpl. Brian Whelan, 21, of St. Francis, Wisc., an Amtrac driver. "It makes it all seem worthwhile."

Intelligence reports had placed the Republican Guard brigade a few miles outside of the town's eastern edge. As the Marines advanced, the first vehicles were fired on with AK-47 assault rifles and rocket-propelled grenades. But they suppressed the resistance quickly and the fighting was all but finished by late morning. The closest most Marines in the battalion came to being shot at was when an arms cache targeted by U.S. artillery was set aflame and began spewing grenades directly over the passing Amtracs.

Most Iraqi forces had already cleared out. Bunkers made from sandbags or dirt berms were unoccupied, and vehicles were left abandoned along the side of the road.

The Marines destroyed several pieces of antiaircraft artillery found along the way and blasted open bunkers with C-4 explosives. They dropped grenades into vehicles that appeared operable and made a bonfire with about 600 abandoned Iraqi rifles.

"We don't want to be shot in the back," Conlin said.

They took at least one prisoner, a man in a green uniform with a white mustache who appeared to be in his late fifties. An identification card signed by President Saddam Hussein was found in his pocket, which suggested, one Marine handling prisoners said, that he was an officer.

Some young Marines who had anticipated a major battle appeared disappointed. "I was told that if I would ever get to shoot my rifle at someone, today would be the day," Lance Cpl. Douglas Sanders said.

Conlin said that it appeared the Iraqis had fled eight to 12 hours before the Marines' attack. "They heard our air and artillery and they beat feet," he said.

Conlin also acknowledged that the Iraqi retreat could be a calculated move, allowing them to regroup elsewhere. "We've gotten reports that many of them changed into civilian clothes when they fled, and we could see them again," he said. "But it appears that our strategy of sapping their will to fight through the air and then following up and destroying them on the ground is working."

Navy Corpsman Romualdo Humarang, with the 3rd Battalion, 7th Marine Regiment, talks with Iraqi civilians while on patrol in Numaniyah, 80 miles southeast of Baghdad on the Tigris River.