BAGHDAD, Iraq — As a young Marine officer leading patrols in Vietnam, John Holly swears he survived by knowing the tangled terrain better than his enemies did. As a private contractor in Iraq dealing with logistics and supplies, he now must navigate a bureaucracy he finds nearly as complex.

Maggie Godson sweated out the 1968 Tet Offensive at an Army fire base as a Red Cross worker sent to boost the morale of frontline troops. Almost 40 years later, the mother of two returned to war, reviewing transportation and facilities contracts in Baghdad.

Charles Thomas was wounded three times in Vietnam — the last time by a rifle shot that shattered his ankle as he stepped off a helicopter into an ambush — and limped home questioning whether U.S. soldiers should have been sent there in the first place. Now in Iraq, he says he is unequivocally proud of his mission.

"What I'm doing now's the kind of thing we should have done more of in Vietnam," said Thomas, 59, from North Potomac, Md., who manages development of Iraq's sewage and water systems. "The thing I regret most about my time (in Vietnam) was we were just plain fighters. We didn't go out and help people with their everyday lives."

Decades removed from the conflict that molded — and, for some, scarred — their generation, dozens of Vietnam veterans have signed up for duty in Iraq. Some are still in uniform, graying guardsmen and reservists activated as part of the largest call-up since the last time most saw combat more than 30 years ago.

But the majority have joined the legion of private contractors working on Iraq's reconstruction. Armed with boots-on-the-ground experience from a war that many believe had devastating consequences for U.S. society, they say their goal is to ensure that Iraq, and the American soldiers fighting here, do not suffer a similar fate.

"We're all over here for pretty much one reason. There's a huge job to do, and we don't want anyone saying it didn't get done right," said Tommy Clarkson, who spent a year in Vietnam with the Army's 44th Signal Battalion and now works as a civilian spokesman in Baghdad for the Army Corps of Engineers.

In his nine months in Iraq, Clarkson has compiled a stack of manila folders, one for each of more than 70 Vietnam veterans he has met, 16 of whom came as soldiers.

Their Vietnam experiences run the gamut: infantrymen, fighter pilots, bridge builders, career counselors.

"Over here, people don't talk much about that stuff — it was a long time ago," said Clarkson, 62, whose wife, Patty, is also a contractor in Baghdad.

"But you see a guy who looks like he could be one of these kids' fathers and you just know, so you ask him, 'Hey, were you over there?' "

Not all of them are guys. Godson, who has been married for 35 years and has two grown sons, came to Baghdad in 2004. She is working overseas for the first time since crisscrossing Vietnam by chopper with other "Donut Dollies," named for the trailers full of pastries and coffee that volunteers traveled with in World War II.

Although there is no tally of how many Vietnam veterans have spent time in Iraq, there are probably barely a few thousand left in the active duty military, according to Rick Weidman, director of government relations for the Vietnam Veterans of America. Many others serve in the National Guard and reserves.

Among the most striking differences between the two conflicts, according to those who have spent time both here and in Vietnam, is the fact that Iraq is under reconstruction while fighting still rages. Another is the dearth of soldiers with wartime experience.

"We used to have these World War II and Korea vets come around, and I would say, 'I am never going to be one of those old farts lecturing the kids about what it was like,' " said Holly, 59, who came to Iraq in 2003 as director for non-construction logistical operations. "Now I figure one of the most valuable things I can do is mentoring.

"I volunteered because I thought I could help prevent another Vietnam. After we pulled out of there, we stuck our heads in the sand like an ostrich, said it was a mistake and we should never have gone. We basically forgot about the place. That would be the worst-case scenario here."