The Marines who helped push Saddam Hussein from power have started to spend their time discouraging looting, patrolling streets and bridges and destroying discarded weapons before they can be used to commit crimes.

"The mission has changed," Maj. Dan Healey, commander of Baker Company in the 1st Battalion, 7th Marine Regiment, told his troops today. "Its like the Wild West out there, and we want to help life get back to normal."

The new posture, Healey acknowledged, requires a high degree of judgment and flexibility on the part of young Marines. No longer are they authorized to treat any Iraqi carrying a weapon as an enemy or destroy any vehicles speeding down the road toward them. Every Marine must assess each individual situation to determine the level of threat.

"A guy with a weapon is no reason to throw him down on his face in the street -- some of them are just trying to defend their families," Healey said. "We have neither the capacity, nor the intent, to keep this place shut down, but there are some things we can do to make it easier to govern."

Traffic flows were restored today over some streets and bridges that had been closed since the Marines arrived in Baghdad on Wednesday. Marines driving on the streets in combat vehicles were told to begin obeying local traffic laws, Healey said.

In the middle-class neighborhood of Jadria this morning, the Marines reopened the 14th of July Bridge, which spans the Tigris River. Two days earlier, residents had helped them set up a roadblock at its entrance and offered them food, tea and hot showers, said Sgt. Stephen Christopher, 23, of Derry, N.H., as he manned a checkpoint near a cluster of stucco homes.

Locals also repeatedly asked the Marines to intervene to prevent looting, Christopher said. But the troops have not been endowed with policing authority, meaning that they could only detain those hostile to U.S. forces. "We don't want to risk the lives of Marines to intervene in every fight between civilians going on out there," Healey said.

The Marines are, however, working with locals to keep their streets safe. Residents of Jadria formed a neighborhood watch in recent days that alerts the Marines to the presence of anyone they deem suspicious. Those found with weapons or deemed dangerous for other reasons are escorted away. Locals said they appreciated the assistance, but that restoring a normal way of life will require more than security.

"We feel safer now than we did, but we still have no electricity and no running water," said a 31-year-old resident and former employee of the Foreign Ministry, who asked not to be identified by name. He said he had not been to work since the war began three weeks ago. "We still feel trapped. They don't always let us come and go as we please."

A few blocks away, residents directed Marines to six Chevrolet pickup trucks with heavy machine guns mounted in their beds, which were stashed under palm fronds on a quiet residential street. Next to the trucks, they found green uniforms with the trademark red triangle of the Republican Guard alongside boxes of grenades and ammunition. A full bowl of rice, a shaving kit and shoe polish were found nearby, suggesting a hasty departure.

"They brought those trucks here right after the American army attacked the airport," said an electrical engineer who lives in the neighborhood. "A few days before the U.S. troops came here, they just left." This afternoon, the Marines began towing the vehicles and their dangerous contents to a more remote location so they could be destroyed with explosives.

"We asked the Marines not to blow them up here, because there are people who live here," said the engineer, a father of three. "We feel safer now than before they got here. Anyone could have come and taken [the vehicles]."

Marine commanders said they recognize that maintaining stability on the streets of Baghdad will be a challenge that will likely outlast their presence in the city. Some units began taking a formal inventory of their equipment today, a process they must complete before packing up to return home.

Meantime, protection of Marines will be the main focus, Healey said, but other priorities will evolve. "We're like a dog that has been chasing a car," he said. "Now that we've caught it, we're trying to figure out what to do with it."

A resident of downtown Baghdad complains to a U.S. Marine that his neighborhood has no protection against looters. Although the troops are attempting to discourage looting, they do not have the authority to arrest perpetrators.