For 40 years, the John Roberts housing project has endured on the western edge of Alexandria's Old Town, in the shadow of the George Washington Masonic Memorial. Its families, first all white, now mostly black, have adorned their sober, red-brick units with flower pots and bright trim, and have watched Alexandria change around them from a sleepy southern town to a sophisticated, affluent suburb of Washington.

During that time, $150,000 town houses, picturesque streetlights and, finally, the Metro tracks have drawn close, making the John Roberts property very valuable--too valuable, some say, for its own good.

Two weeks ago, the Alexandria City Council approved a zoning change that will speed the sale of the six-acre property adjacent to the Braddock Road Metro stop to a private developer. Anticipated sale price: $12 million. The money will be invested by the city's housing authority, which insists it needs the money to avoid bankruptcy and maintain other housing projects.

When new housing is ready, all of John Roberts' 240 low-income tenants will be moved 11 blocks east, near the Potomac River on the north end of Old Town. Forty-five families will be placed in an existing project, which will be rehabilitated and made to blend in with the neatly painted, shuttered town houses nearby. Approximately 45 elderly tenants will be moved to a modern high-rise in the same area. And the John Roberts homes, aging relics from a time when public housing was built to look like poor housing, will disappear.

Lilly Mae Mondy is 64 and has lived in her cramped house at John Roberts for more than a decade. Many of her neighbors have been there much longer, some since the project was built in 1941. Mondy pays $50, roughly 20 percent of her monthly income, on rent and spends the rest of her small Social Security check on groceries, medicine and clothing. The Alexandria Redevelopment and Housing Authority has reassured her that she is guaranteed replacement housing. Nevertheless Mondy and many of her elderly neighbors say they dread having to move.

"It's so sad, I don't even like to talk about it," Mondy said of the move. "This place has been the best thing that ever happened to me," she says. "I'm not worried about vibration from trains. Let 'em come. It's nice and quiet here. Nobody bothers you."

Mondy, a retired domestic worker, rocks back and forth, sits on the edge of a worn upholstered chair in her brightly painted parlor, and sighs. "I don't want to live in any high-rise," she says. "I like my patch of grass. I figured I'd die here. But whatever they're going to do, they're going to do it."

Not everyone in the project will mourn its passing. Many of the families, who occupy half the 90 units, say they won't miss John Roberts' temperamental plumbing and sagging walls.

The sale of John Roberts to keep the rest of Alexandria's public housing solvent is a first for the city. But according to public housing officials around the country, more such sales are likely to occur, not necessarily with replacement housing. Aging housing units, rising operating costs and shrinking federal subsidies are increasingly combining with what officials say could be disastrous results.

Begun in the late 1930s to house Depression families and expanded later to include war workers, the federal public housing program now includes 125 million units. There are public housing authorities in most major cities, all struggling to meet their obligations, and little new public housing has been built in the United States since a Nixon administration moratorium of 1973.

Costs have risen dramatically. Since the energy crisis, housing authorities now spend at least 45 percent of their operating budgets on fuel alone. In addition, federal public housing subsidies, which have been funded at 85 percent since the mid-'70s, are scheduled to drop to 64 percent in 1983.

Among the Reagan administration's suggestions for making up the loss in operating subsidies is that money allocated for rehabilitation of old units be used for operations. The administration also has suggested the demolition and resale of aging public housing units that sit on commercially valuable land, and has targeted 5,000 units for demolition in 1983, according to the National Association of Housing and Rehabilitation Officials.

Some who have spent decades in public housing are frightened by crime and are weary of the vandalism that plagues the project. They long to move. "There's lots of noise here. I don't let my children out alone, what with all the beer and liquor and things going on out there in the summer," says 30-year-old Ella Mabry, a cheerful, energetic woman who has twice won the housing authority's beautification award for the flowers and vegetables she has planted around her three-bedroom corner unit, though vandals ripped up the flower beds last summer.

"Some nights," she says, "I can't sleep with all the confusion, and I just sit up reading my Bible."

The average month's rent at John Roberts is $115. The average annual income per household, $6,500. More than 90 percent of the households are headed by single parents, mostly black women. Although the plumbing is old and unreliable, and the walls cracked and drafty, tenants do not complain much. They know there are more than 1,000 families on the waiting list for public housing in Alexandria, and that the turnover rate is low, 10 percent.

Those who leave public housing have few choices in Alexandria. The vacancy rate is less than 1 percent, an all-time low. Private rental housing for less than $300 is scarce. That makes John Roberts a mixed blessing many tenants are reluctant to give up.

Virginia Shelton is 65, a lifelong Alexandrian and a great-grandmother whose descendants live in the project, too. Seated in the stifling front room, her children and grandchildren watching her with approval, Shelton's anger quickly grows as she describes her feelings to a visitor. In one breath she denounces the move; in the next, the city for housing her family in substandard housing. "I think it's outrageous," she fumes. "They'll do what they want to do. I've been to all the meetings, but nobody asks me what I think! Well I like to be outdoors, I like to be where I can hang my clothes on my own line!"

The impending sale of the project, and the relocation of its 240 low-income tenants, has proven controversial in Alexandria, where elegant town houses and dilapidated public housing sometimes share the same street. It has also raised difficult questions of tenant rights.

The Alexandria Housing Authority argues that the sale of John Roberts is imperative to keep Alexandria's 1,150-unit public housing authority solvent. Without it, Housing Authority Director Angus T. Olson said, the authority will probably be bankrupt in two years.

Rents have not kept pace with increased utility and maintenance costs at Alexandria's 13 public housing sites. At least four of the projects were built before 1945, and badly need rehabilitation. The sale of John Roberts is a necessity, not an option, Olson said. In approving the zoning change two weeks ago, most of the Alexandria City Council agreed with him.

Not everyone bought the housing authority's logic, however. The council's 6-to-1 vote in favor of rezoning was greeted with snorts of derision from a few housing activists who believe the bankruptcy argument is a ploy to wrest a valuable piece of property from tenants who are in a poor position to object. They have argued that the homes could easily be rehabilitated and have solicited blueprints from a team of Howard University student architects.

Council member Nelson Greene, the sole black on the City Council and the only one not running for reelection, cast the dissenting vote. "I don't think time is the important item here," he said at the council meeting. "We probably should consider the people living there. As far as bankruptcy, I kind of don't believe the whole thing anyway."

The sale has also created some surprising alliances. Homeowners in neighborhoods near John Roberts who fear commercial development on the site once John Roberts is gone have also opposed the sale.

One member of the influential Old Town Civic Association sent a memo to the council opposing the planned seven-story high-rise for the elderly, suggesting instead that existing public housing in the northeast section of Old Town be removed and the land be reserved for a "Gold Coast" of privately owned town houses. The Old Town Civic Association has disassociated itself from that memo, and avoided taking any position on the matter.

For now, all is quiet at John Roberts. The tenants will not be moved until their new homes are ready; that won't be for at least a year. Until then, residents like Roosevelt Andrews will watch and wait, with varying degrees of anticipation.

"I think I'd prefer to move to a new place," said Andrews, a 19-year-old who graduated from T.C. Williams High last year, and who has lived in public housing for as long as he can remember. Until he was laid off from his meat-cutting job at Christmas, he hadn't spent too much time around the house. Now he is home most days, drawing, running errands and watching television. When he can, he makes $50 a night as a disc jockey at parties.

Andrews' mother works at a local recreation center. His father is a truck driver and would like his son to follow in his footsteps. But Roosevelt Andrews said he'd like to become an artist, or a deejay. For him, the move into better housing promises better things.

"I don't like the atmosphere here, the busted lights, the confusion out in the alley at night," he says quietly. "I'd like to have a nice house, nice neighbors. My plan is to go back to school and learn a new trade. I don't want to be living off my Mom and Dad forever."