HIT, Iraq — Marine Sgt. Jim Beere knows something about protecting people.

Back home he's an undercover cop in Oakland, Calif., where he works on a special-victims unit tracking rapists and child molesters. He's usually responsible just for himself and, at most, the safety of a partner.

But early on Feb. 22, he saved his own life and quite possibly the lives of a dozen other Marines who were taking a well-deserved catnap after an all-night operation in the city of Hit, 90 miles north of Baghdad.

During the same operation, his platoon had killed two unarmed Iraqis who had failed to obey orders to stop.

The incidents reveal just how much pressure and how little time troops have to determine whether approaching cars mean them harm.

At about 5 a.m., the streets of the city were all but deserted when a sedan turned onto the road leading to the Marines' temporary headquarters in a schoolhouse.

The driver began to speed up toward the Abrams tank guarding the road, so the machine gunner opened fire with two long bursts that sent the car careening into a sewage canal.

The driver, who was hit three times but still alive, rolled out of the car, and Marines ran over to investigate. He was a Syrian who claimed in perfect, almost unaccented English that he'd been forced to drive the car. (He later died on the way to the hospital.)

Beere then went over with another Marine to check out the car.

As the Marine in front of him leaned in the passenger-side front door to take out an AK-47 propped against the steering wheel, a man lunged out of the muck in the canal on the driver's side and went for a rocket-propelled grenade launcher in the back of the car.

Beere pulled his buddy back and to the side, drew his pistol and shot the man five times. The man fell back into the canal.

Beere took a few steps away to catch his breath and, turning back, saw the man coming out of the canal again, this time hitting a "clacker" — a detonating unit for mines and improvised bombs — he held in his hand. Beere shot the man four more times, and he fell dead.

"I thought that was it for me, I really did," Beere said a few minutes later. "The best I can figure is that he had a mine down there with him and was trying to blow up all the explosives in the car. I think the wet ruined the detonator."

This time Beere was right: The trunk was loaded with explosives. But troops don't always make the correct decisions.

The Marines of Beere's Bravo Company, who are finishing a six-month tour in Iraq, have fired on and killed unarmed Iraqis in cars on more than one occasion. In each case, they say, confused drivers either ignored or didn't notice warning shots and shouts to slow down as their cars sped toward Marine positions.

But the suicide car bomb is a favored insurgent weapon at checkpoints. In December, nine Iraqis were killed and 13 wounded by a suicide bomber at a checkpoint south of Baghdad, while in October, 16 people were killed and 40 wounded by a car bomber at a Baghdad checkpoint.

The troops at checkpoints aren't inclined to take chances, and their rules of engagement let them open fire if they feel threatened.

"You feel awful when it happens," says one Bravo Marine, who remembers treating an Iraqi who probably would lose his arm after being shot by the Marine's unit. "But I don't doubt the decision to shoot."