Mobile —- Jimmy Carter strapped on his tool belt and slipped a hammer into its loop like a gunslinger holstering a pistol. As he started to measure a sheet of plywood, a battery of cameras followed every move from a platform 30 feet away.

A familiar ritual of American do-gooding was unfolding. For the 25th straight year, Jimmy and Rosalynn Carter were devoting a week of their tightly booked lives to Habitat for Humanity.

The Carters have become so identified with Habitat that many people think the former president founded the Georgia-based housing ministry.

"When I fly, I'll go around the plane and shake everyone's hand," Carter said during a break this week, his own right hand bruised purple from a run-in with a claw hammer. "It's surprising how many people ask me, not about the Middle East peace process or the health programs we work on at the Carter Center for 51 weeks of the year, but about this one week. They really like those houses we build."

Clearly, the Carters have been very good for Habitat.

The nonprofit organization has grown steadily since they've promoted it, and now builds, renovates and repairs twice as many homes in a year as it did in its first decade and a half put together. In fiscal 2007, that amounted to 49,000 homes worldwide.

Just as clearly, Habitat has been very good for the Carters.

"Habitat jump-started Carter's extraordinary post-presidency," said Douglas Brinkley of Rice University, one of his biographers. "His stock was down when he began working with Habitat. When he picked up that hammer, he started to become a folk hero."

A tradition begins

Carter was 59 and a recently defeated one-term president when he first volunteered with Habitat in 1984.

Now 83, he moves a bit stiffly around work sites and takes more frequent breathers. But the carpenter in him still attacks the job vigorously. Co-workers in Mobile snapped photos of him hoisting plywood like a man half his age.

Carter was running for president in 1976 when Habitat was founded in Americus, a few miles from his home in Plains. The organization grew out of a controversial Christian farming community, Koinonia, where Millard Fuller, a former marketing whiz, and his wife, Linda, decided to devote their born-again lives to eliminating poverty housing.

During their final weeks in the White House, Carter read in the Americus paper that Fuller had criticized him for not attending a Habitat home dedication.

Rosalynn Carter was piqued. "I wasn't sure I wanted to meet Millard after that," she recalled.

But they did, and they were impressed. The former president agreed to serve on Habitat's board, and he and his wife pitched in on a house-raising in Americus.

Their commitment broadened in 1984 when Carter was in New York for a speaking engagement and decided to jog past a six-story apartment building Habitat was renovating in Lower Manhattan.

"It was horrendous," he said. "A dilapidated old building with 330 windows —- all broken —- and the bottom two floors heaped with garbage. People were living on it, building fires to keep warm and cook dope. When I got there, some college volunteers were trying to clean up the mess. On the spur of the moment, I said maybe we should come back and help."

A reporter heard the comment and wrote a story. A few months later, the Carters and 40 others boarded a Trailways bus for New York, where a crowd gathered outside the building to watch and chanted, "Go, Jimmy, go!"

The Carters returned to finish the job in 1985 and decided to make Habitat work projects an annual tradition.

A no-nonsense builder

Over the years, the Carters have helped build homes in 16 states and eight nations. They plan to add to the list next year when the project heads to the Mekong Delta in Southeast Asia.

"They've given me no indication they want to stop," says Habitat chief executive Jonathan Reckford, who succeeded Fuller in 2006.

The Carters have built in South Africa, across the Philippines, and on the tense border between South and North Korea. Their diciest moment actually came in the United States, in the Liberty City section of Miami, where a drive-by shooter missed his target and struck one of their co-workers in the hard hat, inflicting a flesh wound.

"The Secret Service asked us not to work on roofs after that," Carter said. "They said we were too exposed."

Two years ago, during a particularly meaningful week, the Carters built near the village where his mother, Miss Lillian, served in the Peace Corps.

Carter remembers it for another reason as well.

"Brad Pitt showed up on the second day," he said, impressed with the effect his celebrity had on their building schedule. "We finished a day early because so many people wanted to work with him. He worked hard —- just like Garth Brooks did yesterday."

Carter has always been known as a no-nonsense builder.

"That's one hardworking man," said Willie Wilkerson, a vocational teacher in College Park, who has participated in 23 of the 25 projects. He was the Carters' crew chief at one of the first ones, in Charlotte, and has never forgotten the president's suggestion when he saw journalists standing around observing.

"He told me we ought to find something for those writers to do: clean up, move lumber —- something."

A work in progress

The Carters wanted to build on the Gulf Coast to draw attention to the lingering effects of Hurricanes Katrina and Rita. They started last Sunday in Mississippi and moved on to New Orleans. In between, they made a stop in Mobile, where 10 houses were under construction in a working-class area near the University of South Alabama.

Mobile didn't suffer as much destruction as its neighbors to the west, but the storms did pummel its housing market.

"We had so many disaster recovery workers that landlords raised rents," said Brenda Carson Lawless, director of the Mobile Habitat affiliate. "It really hurt low-income people."

One of those affected was excited to learn that the Carters would be lending a hand on her house.

Africa Locke, a 29-year-old divorced mother of two, was having trouble paying $650 a month in rent on her computer programmer's salary.

She signed up for Habitat 18 months ago, attended classes and started working on other people's houses —- part of the required 300 hours of "sweat equity." In return, she'll get a three-bedroom home and a no-interest mortgage with payments of about $350 a month.

"This is going to be the first place I've ever owned," she said. "How many people can say a president helped build their house? I mean, whoa!"

The Carters spent the morning sawing and hammering plywood onto the frame of Locke's house. After lunch, they posed for photos with each work crew and presented each homeowner with a Bible and best wishes.

"I hope we're doing a good job," Carter told Locke, who flashed a Carterish smile back at him.

Then, the Carters strolled toward a van that would take them to Pascagoula, Miss., and another cluster of homes-in-progress. As they often do, the former first couple was holding hands.

ABOUT HABITAT

> Founded in Americus in 1976, it has operational headquarters there and administrative offices in Atlanta.

> Habitat describes itself as a Christian ministry and is nondenominational.

> Homeowners do not get houses for free. They make a down payment and have to qualify for an interest-free mortgage. They're also required to work many hours on other homes as well as theirs.

> Habitat works through local affiliates in 90 countries and 50 states, and with numerous partners such as the Salvation Army and the Home Depot Foundation.