Fallujah, Iraq ? Unlike many Marines in this dangerous city, Staff Sgt. George Scott could have said “no.” He could have stayed home in Ohio with his two young sons.

Pentagon rules limit the number of times reservists like Scott can be called to duty involuntarily. But Scott keeps coming back. He’s on his third tour now, and said he’d volunteer for a fourth.

“I like to be a Marine, leading Marines and being around them,” said Scott, who in civilian life is a car dealer service manager in Orwell, Ohio.

With the war in Iraq still raging after three years and the full-time military stretched thin, the Pentagon is counting on, and courting, committed volunteers like Scott to fill the ranks.

Scott served earlier in Iraq with another unit but volunteered to help the 1st Battalion, 25th Regiment, 4th Marine Division, when it was looking for more troops. Many others also agreed to deploy again: About half of the 500 original members of the 1st Battalion are in Iraq by choice, said Gunnery Sgt. Pete Walz, a spokesman for the reserve battalion stationed in Fort Devens, Mass. The 1st Battalion’s numbers show the increasing reliance on volunteers from the reserves and the National Guard, even as the total number of reserve units is going down.

The extended Iraq conflict, and the Afghanistan fight, have forced U.S. commanders to use reserve forces more heavily than at any other time in recent decades. During the Vietnam War, active duty troops did the vast majority of the fighting. In Iraq, by comparison, the reserve troops made up half of the ground force for much of last year.