Every so often, up above the crumbling houses tangled in ivy and weeds, a Navy jet screams through the sky. The jets sound low enough to land on one of the flat roofs of the hundreds of apartments in Lexington Manor, but most people don't even look up: It's just part of life here.

Patuxent River Naval Air Station, just across the road, permeates everything here -- not just in this Lexington Park neighborhood with broken windows, rotting doors and jet noise -- but across St. Mary's County.

Never is that more clear than when the congressionally mandated base realignment and closure process -- known as BRAC -- looms. Next spring, the secretary of defense will give a list of recommended changes to the president and then Congress.

Business and political leaders in St. Mary's are doing everything they can to keep the base, where the Navy's newest jets are tested, off that list -- including finding a way to wipe out the Lexington Manor apartments, clearing the flight path.

No community wants to lose a military base. Gov. Mark R. Warner (D) formed a commission last summer to find ways to ward off closures. Interstate 64, which leads into the busy Hampton Roads area, was just widened to make it easier to reach the Virginia bases nearby. In Charles County, a community advocacy group hired Washington lobbyists to try to protect the Naval Surface Warfare Center at Indian Head, that county's largest employer.

But in isolated St. Mary's, where the traditional livelihoods of farming and crabbing are dying out, the base feels irreplaceable now. The air station, known as Pax in Southern Maryland, and the defense contractors clustered around it bring good jobs, driving more than 80 percent of the county's economy, according to one study.

If Pax shrank or closed -- "Don't even think about it," said Lawrence D. Jarboe, a commissioner in St. Mary's. "It would be a devastating blow."

Jarboe and others have heard the tales from past rounds of base closings -- how communities were caught by surprise when heavy traffic, failing schools or homes sitting under a flight path tipped the scales for shuttering a base.

So last summer, St. Mary's County leaders made a list of seven priorities for improving the region for the military and perhaps inoculating the base against changes. They'll make another this summer, crossing off their progress so far: Roads widened. Schools funded. And now the Lexington Manor redevelopment, a nearly $14 million project to be paid for with county, state and federal money.

The efforts to protect the base touch nearly everyone in the county, as political rivals cooperate, massive projects are funded and decades-old problems are solved. Not only has Pax shaped the culture and the landscape here; over the years, this small corner of the county has drawn in most of the money and power.

Across the street from the base, where rows of houses spray-painted "KEEP OUT" slowly decay, there's very little of either.

"I'm living on borrowed time here," said Vanessa White, a Lexington Manor tenant. "We got to go because of the planes."

She's lived for 35 years in this neighborhood, better known as the Flattops for its roofs like the deck of an aircraft carrier. "I've seen it all, sitting right here," she said from her seat looking out over her lawn, with the crape myrtle her parents planted as a seedling now 15 feet tall and bursting with pink flowers.

The Navy built the 342 homes, squat little houses for enlisted men, in 1944, and sold the Flattops to a private company in the 1960s. Over the years, the houses wore out. When Essex South Management LLC bought the 84-acre property in December, it tackled repairs and spent months just hauling tons of trash out, said Tom Watts, the managing partner. "It was dismal," he said.

Most of the Flattops are abandoned now. Some of the cream-colored cinder-block homes have a fringe of grass and weeds growing along the roof like a second lawn, or orange mesh covering shattered glass in the windows. A washer rests in one yard; a sofa outside gathers mold.

About 80 of the homes have tenants, people who can't afford anything else, who hang sheets over windows for privacy and keep spraying the linoleum floor to try to keep the roaches away.

Officials have worried for years about risks there, including the danger posed by Navy planes. The homes are in the flight path, an area on which the military placed restrictions in the 1970s. And when Secretary of Defense Donald H. Rumsfeld listed criteria to be considered in the next round of base readjustments, such encroachment was one of them.

The defense secretary will give a list of recommendations for saving money and improving efficiency to an independent commission in May. By September 2005, the base realignment commission will forward a report to the president, who can only approve or reject it as a whole and then forward it to Congress, which must do the same.

Local government can't improve military efficiency at the base. But those factors that leaders in St. Mary's can control, such as roads and schools, they have worked to change. Local, state and federal leaders gathered this month to celebrate the completion of $75 million in improvements to Route 235, the main road through Lexington Park which became swollen with traffic in the early 1990s when base closings elsewhere brought an influx of jobs and people to the base.

County commissioners gave school officials everything they asked for in this year's budget and made sure new schools will be built.

For years, developers and county leaders have argued about the Flattops. Recently, a settlement was reached in a lawsuit on the matter that allows the county to buy the land by Aug. 16. But the money -- millions for the property, demolition, resettlement of tenants and rebuilding -- was never a priority, until concerns about base closings pushed the project to the fore. The county will spend about $5.1 million, said John Savich, director of the county's economic and community development, and the rest will come from state and federal grants.

The land will be redeveloped, perhaps as a park at the southern end closest to the base, perhaps commercially at the northern end.

Demolishing the Flattops will worsen the county's shortage of affordable housing. Most places White has seen are easily two or three times her $400-a-month rent for a three-bedroom apartment. So even though the county has promised to help people find new homes and cover the difference in rent for several years, as it is required to do by law, many Flattops tenants are skeptical.

St. Mary's will build 142 new homes, mostly apartments, nearby in the next few years.

"We will hopefully get the residents -- after the disruption of having to move -- into better housing," Savich said. "And the Navy will see that their greatest community-related concern, the encroachment problem, has been dealt with. So going forward when the Navy thinks about experimental aircraft programs, they'll see the community acted to reduce the risk."

Vanessa White examines the mildew and water damage on the house in Lexington Manor where she has lived for 35 years and which she will probably have to leave. "I'm living on borrowed time here," she said.