Thirteen companies are seeking state approval to build nursing homes in Northern Virginia, an affluent area with an aging population and a severe nursing home shortage.

There are currently 17 nursing homes and four life care centers in Northern Virginia, with a total of 2,980 nursing home beds.

Fairfax County officials estimate that 950 more beds will be needed by 1990. The state has already agreed to approve an additional 430 beds, which would mean construction of about three to five new facilities.

Of the 13 proposals, Fairfax County government officials and a citizen's advisory board have recommended that the Board of Supervisors throw its support behind three of them:

* A 120-bed nursing home in Reston by Medical Facilities of America;

* A 90-bed nursing home in Franconia by Manchester Lakes Associates, which would be part of a 170-bed "life-care" program that would also include apartments and cottages;

* And a "life-care" facility developed by Goodwin House II in Baileys Crossroads.

"We looked at a variety of things," said Mary Grace Lintz, a member of the Fairfax County Health Care Advisory Board. "We looked at the need for nursing home beds, especially in areas with high numbers of elderly and no nursing homes. We looked at their (the firms) track records or reputations . . . and their willingness to accept Medicaid patients."

The advisory board recommendations, which the supervisors are scheduled to review today, are expected to generate some controversy because the advisory board declined to back a Reston nursing home proposal by the Fairfax Hospital Association, a not-for-profit group that has a monopoly on hospital care in the county. The advisory board expressed concern about the Fairfax Hospital Association's lack of experience in the nursing home field.

The Health Systems Agency of Northern Virginia plans to hold hearings next month on the applications and will forward its recommendations to Virginia Health Commissioner James B. Kenley, who will make the final decision near the end of the year.

According to a recent study by Fairfax County, "the supply of nursing home beds, and particularly those for Medicaid eligible people, is not adequate to meet the need for services."

That shortage was exacerbated by a two-year moratorium on new nursing home construction. The cap, which was lifted July 1, was imposed by state officials because of a nursing home surplus in Virginia. But Fairfax County officials said the surplus was in other parts of the state, and that even back then, Fairfax nursing homes were full.

Of the existing nursing homes in Northern Virginia, eight are in Fairfax County, one in Alexandria, three in Arlington County, three in Loudoun County and two in Prince William County.

Three of the facilities in Alexandria and one in Fairfax are life care centers, which provide a wide range of housing from apartments to cottages to nursing homes. In most life care centers, the resident pays a large entry fee and monthly payments, and then moves around to whatever setting is most suitable at the time.

The highest concentrations of elderly in Fairfax are in Falls Church, Baileys Crossroads, McLean, Alexandria, Mount Vernon, Vienna, Springfield and Reston, according to county staff members. But there are no nursing home facilities in Reston and in the Springfield area. Residents in other areas have relatively close access to one or more nursing homes.

A major concern of the advisory committee, according to Lintz, was some nursing homes' practice of accepting private-pay patients before Medicaid patients because Medicaid patients often pay less and their care involves more paperwork. Thus the advisory board and county staff members placed considerable weight on the applicants' commitment to serve Medicaid patients.

Currently the county has no way to enforce such promises, and the advisory board recommended a two-pronged approach: state legislation to prohibit nursing homes from discriminating against Medicaid recipients and a county requirement "as a condition of zoning approval that nursing homes adhere to their commitments to serve Medicaid patients on a first-come, first-served basis."

"Some nursing homes will tell you they can't make money on Medicaid patients," said Lintz. "But Virginia is a prime state where nursing home companies want to build," particularly Northern Virginia.

"There are 13 applications, indicative of its being an attractive area," said Lintz, noting that many of these are for-profit chains that already handle a substantial number of Medicaid patients.

She argued that if they were losing money on these patients, the firms would not be anxious to expand in the state.