Rental apartments in Fairfax County are hard to come by, particularly new, attractive ones.

No rental apartment buildings have been built in the county without federal housing subsidies in the past eight years, and many of the county's older apartment complexes have been converted to condominiums in the intervening years.

The County Office of Research and Statistics reported that the vacancy rate is running at about 2.6 percent, and county officials are scrambling to find other ways of meeting the housing needs of low- and moderate-income residents who cannot afford to buy housing in Northern Virginia's high-priced market.

The county recently changed its zoning ordinance to allow people to rent accessory apartments in their own homes, but housing officials say they do not believe that allowing so-called "granny flats" is a solution to the apartment shortage.

The true culprit is the high cost of financing, almost everyone agrees. And as interest rates have dipped in the past few months, some developers are beginning once again to consider building apartments.

But some builders as well as county officials say the county itself is to blame for not zoning land over the last decade to accommodate multifamily rental developments. They say this shortfall in zoning could defuse any recovery of the apartment construction business.

"It's been an interesting wrinkle that, because building rental apartments has not been financially feasible over the past 10 years, there has also been little planning for apartments on the county level," said Michael Was, vice president for marketing at Reston Land Corp. "There are actually very few sites in the county zoned and planned for multifamily developments."

Was said that Oxford Development Corp. of Landover is planning to build an apartment complex on a parcel of land in the heart of Reston, but he indicated that the site has been planned for apartments since Reston was conceived. Moreover, he pointed out that Reston's overall master plan has helped preserve land in the community for apartments.

Most of Fairfax County has not been planned as carefully as Reston was, and officials with the Fairfax Housing and Redevelopment Authority agree that land appropriate for apartments is in short supply.

"We have a difficult time finding land that is zoned for multifamily apartments--meaning that you are looking for something that will allow 20 units per acre or more--and which is also adequately serviced by transportation," said Michael Scheurer, senior housing development planner with the housing authority. "The biggest issue in trying to encourage development of apartments in Fairfax County is finding land and financing."

Scheurer said the urban centers in the county, such as Tysons Corner and the Rte. 1 area, are particularly short of land available for apartment complexes.

"There is land zoned for mixed-use development near these employment centers, but that does not guarantee there will be rental units there," said Scheurer.

But planners argue that just because there isn't a lot of land zoned for high-density residential units doesn't mean the county comprehensive plan cannot be changed.

"We haven't lost track of planning for rental units," said Theodore J. Wessel, director of the county Office of Comprehensive Planning. "We have always been concerned about the shortage of apartment units and have tried to encourage and accommodate developers so that they will include them in their plans."

Wessel said his planning staff consistently has recommended against changes in site plans that would replace apartments with condominiums or town houses. But he noted that, because apartments have not been financially feasible to build in the past, it has been difficult for the county to hold developers to plans that included apartments.

Peter Johnson, director of the county's Land Use Planning Office, said the purpose of the comprehensive plan is not to address ownership--whether a housing unit is occupied by the owner or rented to others--but to accommodate low- and moderate-income families. County planners say their plan does accommodate these income groups, primarily by allowing higher densities for developers who provide units for lower-income people.

But developers say attempts to rezone land for high-density residential complexes in the county traditionally have presented problems, particularly if the land has not been planned for such a use. Developers claim that local residents often are unhappy about the potential impact of a high-density development on traffic and social services.