No "For Sale" sign hangs in front of the decaying Arna Valley apartments in south Arlington, but the people who live there aren't so sure.

Although the owners say the 584-unit complex isn't on the market, dozens of residents there are worried that Arlington's rapidly spreading development could force them to move. They have begun discussing ways to encourage a new owner to preserve as much low-cost housing as possible.

"We can look around and see development all around us, so we know it's only a matter of time," said Sherry Walker, an Army Department secretary who said she leases a one-bedroom Arna Valley apartment for $425 a month.

"I can't afford to pay $675 a month like other places want. Arna Valley's a large chunk of the affordable housing around here, and if it sells, a lot of people will have to go as far as Prince William for a place to live."

Walker's concerns are shared by low- and moderate-income residents throughout south Arlington, where relatively cheap land has attracted developers who want to build new, more expensive housing in what has been the county's most affordable area for decades.

County officials, residents and developers acknowledge that redevelopment of prime south Arlington tracts such as Arna Valley's location at South Glebe Road and Interstate 395 is inevitable.

The challenge, officials and residents say, will be to persuade developers to preserve significant parts of their projects for housing that is "affordable." County government's definition of affordable means that four-member households with annual incomes of up to $40,800 would pay no more than 30 percent of their income in rent.

At stake are the county's commitment to preserve residential areas for its working-class residents, as well as efforts to maintain the character of south Arlington neighborhoods such as Nauck, a historically black area where recent development of new homes and town houses is bringing in younger, wealthier residents.

"We know this area is ripe for {developers} to come in and build homes that price people out of Arlington," said County Board member William T. Newman Jr. (D), a south Arlington resident. "It's an ongoing and growing problem."

For years, Arna Valley residents have heard rumors about a sale of the 50-year-old complex, which is home to hundreds of government workers, immigrant laborers and students. Residents' concerns have heightened in recent months, as maintenance problems and a proliferation of three-month leases -- rather than ones for longer periods -- have cast doubt about Arna Valley's future.

"The complex is so deteriorated and so poorly managed that it begs the question of whether the owners are cutting their losses and are ready to sell," Arlington housing activist Victoria Luna said.

Officials of Stone Properties, Arna Valley's owner, say they are working to correct maintenance problems and do not have plans to sell the apartments. But county officials say that in the past two years, three developers have expressed an interest in the property, which now has an assessed value of about $25 million, up more than 33 percent since 1988.

At a recent Arna Valley street festival peppered with ethnic foods and Latino music, residents spoke about their fears for the complex's future.

"This is just about the only place I can {afford to} live," said Pastor Lazo, a construction worker who shares a simple one-bedroom apartment with his wife and two children. "We look around, but no one will take children. Sometimes I think it might be better to leave {the Washington area}. We can't take much more of this."

County Board members this month will consider adopting a housing plan for Arlington that is expected to stress ways to keep some areas of the city affordable for blue-collar workers like Lazo and others who can't otherwise break in to the county's housing market.

A draft of the policy released this spring urges the creation of 3,600 "affordable" units during the next 10 years. Because Arlington has no public housing or a housing authority, much of the job will be left to private developers and nonprofit groups such as the Arlington Housing Corp. The draft also recommends that the county offer developers incentives and consider granting loans for construction of low-cost housing.

County Board Chairman Albert C. Eisenberg (D) said any redevelopment of Arna Valley would evoke memories of Lee Gardens, an apartment complex near Route 50 and Court House Road that showed Arlington officials just how costly preservation of such units can be.

After the Artery Organization, a Bethesda developer, bought Lee Gardens in 1986 and announced renovation plans that would have forced up to 3,000 tenants, most of them low-income Hispanics, to move, Arlington officials began negotiations to prevent as much displacement as possible.

Artery eventually agreed to sell a part of the project and donate $1 million toward its renovation. Federal rent subsidies were obtained and bond financing of $33.6 million was granted by the Virginia Housing Development Authority for purchase and renovation.

The Arlington Housing Corp. now owns the 364 units of the complex known as Woodbury Park. The rents on 200 of those units are federally subsidized so tenants do not spend more than 30 percent of their income on housing.

"It was an extraordinary situation, and we had to do something," Eisenberg said. Arna Valley "could be another Lee Gardens," he said.

In Nauck, a traditionally black area of modest homes just across I-395 from Arna Valley, residents say the sale of individual houses to developers and the construction of dozens of $200,000 town houses on South Glebe Road are threats to the neighborhood's heritage.

Those changes, and recent plans for 51 new town homes starting at $150,000 near South Glebe and Shirlington roads, cause some to say that young people -- particularly young black families -- are being priced out of the area.

Eisenberg said he doesn't blame residents of Arna Valley and Nauck who are concerned about the decreasing supply of low-cost housing.

"The scarcity of housing here creates a certain atmosphere," Eisenberg said. "People will always be looking over their shoulder to see what might be gaining on them."