Marines picked their way toward central Baghdad today, rolling across a tributary of the Tigris River and taking control of an expansive industrial complex southeast of the Iraqi capital.

Overnight, combat engineers erected a floating steel bridge over the waterway, the Diyala River, to replace a structure the Marines had destroyed with explosives after finding it sabotaged. At the break of dawn, a convoy of armored vehicles streamed across and secured a foothold in an area that was a mix of slums and farmland on the other side after a brief gun battle. The convoy then moved west along a ridge road flanked by buildings ravaged by small-arms fire, artillery and aerial bombardment.

"So far we have been dividing the area into zones of responsibility for each of our battalions, and then clearing them one by one," said Maj. Dan Healey, commander of Baker Company in the 1st Battalion, 7th Marine Regiment. "Today was about enabling further passage into Baghdad."

On all sides, truck fires belched black smoke into the sky and virtually every building was riddled with bullet holes. Large patches of earth were scorched. A dead body, stripped of its clothing, lay face down in a field. Another in the road was run over by several of the vehicles as they passed.

As the convoy approached a vast industrial campus covering dozens of acres along the Tigris,, small-arms fire began to whistle overhead. Intelligence reports had indicated Iraqi forces were using the facility to launch attacks on U.S. Army troops on the other side of the river.

The vehicles arrived at a series of large warehouses and discharged their infantry to begin clearing the compound. Almost immediately, the air was filled with gunfire: The pop of M-16 rifles and intermittent cracks of responding AK-47 assault rifles were nearly drowned out by the staccato of .50-caliber machine guns.

Marines used shotgun blasts to open locked doors as they passed from building to building. An unarmed, elderly security guard who ducked into a hut and attempted to make a phone call was apprehended for questioning by interrogation specialists. Tanks rumbled up and down the streets, providing support for troops.

Marine snipers played a major role in the operation, moving catlike along the rooftops, searching out enemy targets. They reported having killed between nine and 14 Iraqi defenders.

One Marine sniper was injured when part of a fiberglass roof collapsed and he fell 50 feet to a concrete floor below. He sustained a gash on his head, a fracture that poked through the skin of his right leg and two broken arms. But he was conscious and alert when he was found by a group of Marines patrolling the warehouse, which was full of construction equipment and furniture. His name was withheld pending notification of his family.

Four Navy corpsmen who serve as medics for Marines rushed to the scene, stabilizing his leg with a wooden splint and placing him on a backboard. His face was caked in blood. They cut off his camouflage uniform and boots to treat his wounds and had him stabilized by the time the battalion surgeon, Richard Clark, arrived along with Lt. Col. Christopher Conlin of Falls Church, who commands the battalion.

"When you get to the hospital tell them you made it all the way to Baghdad," said Conlin, his hand on the wounded Marine's shoulder. "You're going to be fine."

The sniper's partner, who said the two of them "do everything together, from shaving to eating meals," was visibly shaken but cheered when his partner began to joke about his condition.

"Will I still look pretty?" the wounded Marine asked as he was carried outside to a UH-60 Black Hawk helicopter that had swooped in to evacuate him to a nearby Army surgical company.

"You're a very strong patient. It made our job easier," said HM2 Jaimer Cadang, 27, of Oxnard, Calif., one of the corpsmen who held an IV tube full of painkillers for his patient. "That was quite a fall, and we're lucky it wasn't worse."

As the Marines continued their search, at least two other Iraqi gunmen were killed. The Marines also said they found two dozen AK-47 assault rifles stashed in various rooms and what one staff sergeant described as "boxes and boxes" of gas masks, chemical protective suits and injectors filled with atropine, an antidote to nerve agents. The Marines threw the AK-47s onto the ground and destroyed them by running over them with a tracked vehicle.

Just outside the industrial complex, they found a battery of 12 antiaircraft guns and a cache of ammunition. They destroyed some of the ammunition with hand grenades, touching off a brief "cook off" that sent rounds sailing in all directions while the Marines took cover behind a berm. In the late afternoon, they rigged the antiaircraft guns with C-4 explosive and destroyed them in ground-shaking blasts.

In the early evening, the Marines took a few hours to relax, some sipping sodas they found in a bottling facility, while others dismantled AK-47s they hoped to take home as souvenirs. After several long days in a row, many said they were weary and eager to get the conflict over with.

Corpsmen reported that many Marines were coming down with trench foot from the sweltering weather and a couple of days of wearing their rubber chemical protective boots earlier in the week.

"The guys are pretty smoked," said the Healey, 36, the Baker Company commander, of Worcester, Mass., after huddling with platoon commanders to plot their defensive positions for the night ahead. "But they have a lot to be proud of; we've had a productive couple of days."

Members of Lima Company of the 7th Marine Regiment take positions along a runway during an operation to take over Rashid air base near Baghdad as U.S. forces moved throughout the city. Lance Cpl. Thomas J. York of Carthage, Ind., searches a house while securing a main road southeast of Baghdad.A Marine from the 3rd Battalion, 4th Marine Regiment, searches an Iraqi civilian on the outskirts of Baghdad.