CHARLOTTE, N.C. -- For the fourth consecutive summer, former president Jimmy Carter traveled by chartered Trailways bus to a hot and sticky inner-city slum, checked into spartan dormitory quarters and spent a week as a volunteer carpenter on a housing project for the poor.

As in previous summers, Carter was working with Habitat for Humanity, the Americus, Ga.-based ministry that sponsors the building projects.

The former president, who said he could think of no better way to spend a vacation, told coworkers in Charlotte, "I guarantee you, the sacrifice you think you've made will turn out to be one of the greatest blessings of your life. This is the most exciting, challenging, unpredictable and gratifying thing I've ever done."

Carter wasn't alone in his enthusiasm for what the group said was Habitat's most ambitious effort -- to build 14 houses, covering an entire city block, in just five days. The people of Charlotte seemed to jump at the chance to become known for something other than the scandals of Jim and Tammy Bakker's PTL ministry.

About 350 other volunteers from 28 states and two Canadian provinces picked up saws and hammers on July 26 and followed Carter and his wife Rosalynn to a struggling section of the city known as Optimist Park.

Enduring the stifling summer heat and 10-hour work days, the group transformed three acres of concrete foundations and piles of lumber into a village for more than a dozen needy families.

Bobby Darby, a plumber's helper, and his family will move into one of the homes he helped Carter build. Because of the Habitat program -- which includes a no-interest 20-year mortgage that will mean payments of $150 a month -- the Darbys will be able to afford a new three-bedroom home. They now live in a cramped one-bedroom apartment, where one of the children shares a bed with Darby and his wife and the others sleep on the floor.

"It's a great feeling," Darby said. "When they say this is a miracle, it really is."

During previous Carter work parties in New York and Chicago, the construction activities of the Christian group were regarded largely as a curiosity.

But in Charlotte, a powerful alliance of church, business and civic leaders organized long before the Carters' arrival assured that the project would be one of the most effective of the 204 programs run by Habitat throughout the country.

For weeks before the event, callers deluged the Habitat office with offers of help. Churches lined up for the privilege of feeding 350 volunteers at the end of each work day. Others provided bag lunches that contained personal messages of inspiration written by members of youth groups. Businesses donated everything from free billboard space to film.

Inspired by the example of John Crosland, chairman of the local Habitat board of directors and a developer whose firm builds more houses than any other in the Carolinas, 16 Charlotte companies contributed $50,000 each as part of the project's "Master Builder" fund-raising effort.

Other companies made large in-kind donations, ranging from materials and the complete installation of plumbing, electrical and heating systems for all 14 houses to the planting of $12,000 worth of trees by a local nursery.

A local Pepsi-Cola company donated about 10,000 cans of soft drinks that were consumed by the workers.

Two TV stations in the city provided extensive coverage and even assigned reporters to work as volunteers.

One station conducted a telethon with the goal of raising $25,000 for the project. The campaign went off the air after receiving pledges totaling $33,000.

In addition to businesses, a number of churches gave significant contributions -- including $150,000 from Christ Episcopal, more than $75,000 from Covenant Presbyterian and $25,000 from the Roman Catholic diocese.

In a thoroughly ecumenical gesture that crossed not only religious but also political borders, Joseph Chambers, the outspoken fundamentalist pastor of Paw Creek Church of God, turned out to work the entire week with Carter, despite the pastor's fervent support of President Reagan.

Millard Fuller, founder and executive director of Habitat for Humanity, called the coming together of different churches "the fulfillment of a dream that I've long had for the whole nation and the whole world . . . .

"We can agree to disagree on matters such as when and how to serve communion, what the preacher should wear and whether he should even be a she, but come together when it comes to serving the poor, taking our Sunday school lessons out of the classroom and bringing them onto the street."