In Iraq, Capt. Paul Peterlin commanded a California National Guard transportation team that logged 400,000 miles, frequently under attack by roadside insurgents.

Here in post-hurricane New Orleans, the 35-year-old father of three from the Sierra foothills city of Grass Valley, Calif., heads a military police company at Louis Armstrong International Airport processing thousands of evacuees and dispatching patrols into the city to look for survivors and victims.

“This is a case of the National Guard doing what we were set up to do,” said Peterlin, a stocky UC Davis graduate with a degree in history. “We are helping our own country here. In Iraq, it was harder to understand what was going on or whether we were helping or not.”

On the ground in New Orleans, where Times reporters were embedded with the 726-soldier California National Guard Hurricane Katrina Task Force last week, soldiers generally spoke enthusiastically of their relief efforts in Louisiana.

“I’m very proud to be here. This is what we are all about,” said Maj. John McBrearty, 45, of Riverside. McBrearty, who in civilian life is a screenwriter, served as executive officer with the San Bernardino-based 1st Battalion 185th Armor at Camp Scania, a forward operating base south of Baghdad.

“The cool thing about New Orleans,” said Lt. Jerry Gold, 35, of Ione, about 30 miles southeast of Sacramento, “is that my troops were all fired up to do the work. In Iraq, morale was a big issue.”

Several hundred of the California soldiers in New Orleans, particularly with the 2nd Battalion 185th Armor out of San Diego and the 870th Military Police from the Bay Area city of Pittsburg, have had recent service in Iraq.

Some, like Gold, a Marine before joining the Guard in 1998, served in the Gulf War and the Iraq conflict.

Mixed with their satisfaction about the work in Louisiana was residual bitterness among many soldiers from their time in Iraq — unexpectedly long tours, which many said destroyed marriages and disrupted their civilian careers.

“When I left for Iraq,” said Staff Sgt. Thomas Neal, 41, married father of three from Galt, just north of Lodi, “I was safety manager for a construction company making about $75,000 a year. When I came back, the company said they could no longer guarantee me a 40-hour week. I ended up having to leave the company that I worked with for 12 years.”

Spc. David Walter, 44, of Vacaville, who in civilian life is a corrections officer with the Solano County Sheriff’s Department, said assignments like hurricane relief were what he had in mind when he signed up for the Guard five years ago.

“When I joined, I thought we were like the minutemen,” Walter said. “We are the last defense on American soil. In five years, it’s changed. We’re now front-line. We’re almost part of the Army.”

The California soldiers’ duties in the muggy New Orleans heat ranged from neighborhood patrols to animal rescue missions.

When Peterlin arrived at the airport Sept. 2 with the 119 soldiers in his military police company, he immediately found himself thrust into New Orleans’ volatile political scene.

“We came in a tenuous situation where the local [Jefferson Parish] sheriff had closed the airport to evacuees,” said Peterlin, who in civilian life is an emergency services investigator. “We teamed up with Louisiana state troopers and basically came in and took the airport. The Sheriff’s Department had blocked entrances, and we had to remove barriers.”

Once in control of the airport, the MPs found what Peterlin described as “near riot” conditions as several hundred tired and hungry evacuees threatened to overrun the handful of federal border agents who were manning the crowded airport terminals.

The soldiers organized the evacuees into lines that at one point stretched for more than a mile. After several days, they had fed and processed more than 40,000 people and organized their transport to other cities.

On one steamy afternoon, one element of the MPs was assigned to escort a task force from Orange County wading through stagnant, foul-smelling floodwaters in house-by-house searches on a remote peninsula in St. Bernard Parish, about 20 miles southeast of central New Orleans.

The houses were a contrasting mix of trailer homes and expensive two-story brick structures in developments with French names such as Terre Aux-Boeuf Estates.

“It’s getting pretty gnarly out there,” said task force leader Marc Hawkins, who back home is a battalion commander for the Orange County Fire Department. “We have cottonmouths everywhere, mosquitoes as big as my head and even had an alligator.”

The Guard’s role as security provider was put to the test on several occasions. On foot patrols that fanned out through muddy streets, soldiers burst through front doors left open by fleeing residents and stood at armed guard before public buildings.

Sept. 11, when a cloudless sky unleashed the late-summer sun on New Orleans, a squad from San Diego’s 185th Armor Battalion heard what might have been gunshots ring from inside Samuel J. Green Junior High School, on the edge of the Garden District. The soldiers spread out, some taking cover behind abandoned cars caked in black mud, others bursting through the school’s front doors.

“California National Guard — anybody in there?” one soldier yelled from a second-floor classroom.

“Come on out with your hands up if you’re in there,” another soldier screamed a few minutes later.

But no one was in there, at least not by the time the squad reached the school’s third floor and found empty cans of tuna and a cigarette left burning by someone who had left through an exit to the roof.

“You can tell people had been there; they were probably just a little faster than we were,” said 1st Sgt. Ed Martinelli of San Diego.

When asked if, over his 26 years in the National Guard, he had ever done something like this on American soil, Martinelli was quick to answer.

“Probably not on this volume, not even in the L.A. riots,” he said. “You’ve really got to be a little careful; you’re not sure what you’re going to walk into.”

Tempest is a Los Angeles Times staff writer. Lillis is a writer with the Los Angeles Times UC Berkeley Graduate School of Journalism California National Guard project. Additional stories in the series can be found at latimes.com/guardgoes.