Plans to revitalize Northern Virginia’s aging suburbs will eliminate thousands of affordable rental units and price out low- and moderate-income families, according to a report released Tuesday by a housing advocacy group.

Local governments are replanning the adjacent communities of Columbia Pike in Arlington County, Baileys Crossroads in Falls Church and the Beauregard corridor in Alexandria. Officials envision older strip malls and parking lots being converted into urban town centers served by mass transit.

Of the 25,000 rentals in the revitalization areas, more than 11,500 are low-cost units that are at risk, according to the report by the Northern Virginia Affordable Housing Alliance.

Built at least 40 years ago, the units are part of privately owned apartment complexes that receive no public subsidies. Owners are free to redevelop as the areas around them change.

“When aging areas redevelop, usually we lose housing stock. Everything that comes in there is newer and more expensive,” said Michelle Krocker, executive director of the housing alliance.

Affordable units are ones that can fit into the budget of households with incomes below $82,800, or 80 percent of the area median income, according to federal standards. Based on that standard, the maximum affordable rent for a three-bedroom apartment is $1,603 to $1,664.

In their replanning efforts, the Alexandria and Arlington County have identified the need to retain or replace low-cost rentals. And as Baileys Crossroads redevelops, Fairfax County plans to set aside some new units as affordable or workforce housing.

But according to the report, the three localities lack aggressive strategies for preservation of affordable housing. The study urges them to create incentives — such as tax breaks or small loans used to renovate units — for apartment owners to maintain lower rents.

“We’re talking about private owners who can do whatever they want with their buildings,” said Angie Rodgers, the report’s author. “As these plans ramp up, then its important for these jurisdictions to position themselves on how they want to preserve this affordable housing.”

Providing tax incentives to apartment owners is one tool being considered by Arlington, said Christopher Zimmerman (D), chairman of the County Board and a Columbia Pike resident.

“We’re trying to get a plan and a set of tools in place that make it worthwhile for people to work with the county,” he said. “We’ll partner with anybody to get affordable housing.”

Older apartment communities have helped Columbia Pike, Baileys and Beauregard remain affordable, making them attractive destinations for immigrants. These neighborhoods, according to the study, include higher percentages of minority households. About 57 percent of the Beauregard population is nonwhite — mostly Asian, black and Latino — compared with 46 percent in all of Alexandria. And Baileys is part of Fairfax’s Mason District, where 47 percent of housesholds are nonwhite, compared with 37 percent overall in the county.

Because of rising rents and condominium conversions, cheaper units are becoming scarce. Over the past decade or so, the report says, Arlington County lost about 11,000 low-cost units, Alexandria lost an estimated 10,000, and Fairfax County lost about 8,000. And with job growth, there are more renters competing for the declining stock.

More than half of the 11,500 units the report says are at risk are located in the Columbia Pike area. Since 2003, Arlington County has led an aggressive effort to replan Columbia Pike into an urban neighborhood with mixed-use development. Today, the area is home to new luxury apartment complexes that include street-level retail establishments and services such as valet dry cleaning. The average rent is $2,155 per month for the newer high-end units in South Arlington, including Columbia Pike, according to Delta Associates, a real estate analysis firm.

Affordable housing developers are trying to save Columbia Pike’s supply of cheaper rentals.

This month, the nonprofit AHC Inc. announced it has a contract to purchase Magnolia Commons, a 198-unit apartment community built in the 1940s. AHC has developed about 2,700 affordable units in Arlington.

Preserving affordable housing is a challenge, said John Welsh, director of the multifamily division at AHC. “A developer coming in with an all-cash offer could redevelop the property, dislocating all of the residents and increasing the rents,” he said.

Development plans for the area include a street car on Columbia Pike with two stops in the adjacent Baileys neighborhood. Fairfax County has similar plans underway to redevelop Baileys into a town center.

In nearby Alexandria, city officials are replanning the Beauregard area, home to the Mark Center, where 6,400 federal employees will relocate under the Defense Department’s Base Realignment and Closure process. Companies there have created conceptual plans to redevelop aging apartment buildings into dense neighborhoods within short walking distance of new shops and restaurants.

Stewart Schwartz, executive director of the Coalition for Smarter Growth, said saving affordable rentals will allow lower- and moderate-income workers to have better access to transit and live closer to major employment centers.

“For too long, we separated housing and jobs and, in particular, pushed housing far from jobs,” he said. “We need all levels of the work force if our economy is going to succeed.”