Jean Moylan no longer worries about cold floors or the rent rising beyond her limited ability to pay. She's not scared or lonely, like she was a year ago.

That's when the gregarious 66-year-old woman moved into an efficiency in the Lincolnian, a light, cheery Fairfax County-run residential facility for low-income seniors in Annandale. Moylan's modest rent, pegged to her income, includes all utilities except the telephone.

Mary J. Nardino's savings from her years as a bookkeeper gave her more options on where to live. But she and her son hunted for almost two years before they found Little River Glen, the county government's newest retirement facility and the first one for seniors with moderate incomes and up.

"I was worried my money wouldn't last, but here I should be protected from big rent increases," she said.

Moylan and Nardino are part of a rapidly growing sector of the Northern Virginia population over 60 called the "young-old," a term that applies not so much to a specific age group as it does to a high degree of independence. The young-old are active, able to care for themselves and mentally sound. They span all economic levels including some of the most financially well-off people in the area. Although most are on fixed incomes, about a third are still employed.

The young-old are the fastest-growing group in suburban Washington. Area planners estimate that about 150,000 live in Fairfax and Arlington counties and in Alexandria, twice as many as 20 years ago. The number is expected to triple in 10 years.

As the group grows, government and industry are lining up to meet its housing needs with specially built "independent living" rental facilities. Those facilities also serve as bases for health, transportation and recreation services offered by local jurisdictions.

Independent living units in Northern Virginia rent quickly, and there are waiting lists for many, although more than 80 percent of seniors nationwide prefer to live in their own homes, according to the American Association of Retired Persons.

Fairfax County is way ahead in the independent living game. In the last five years, the county has built more than 200 independent living apartments for low- and moderate-income seniors in four locations: Annandale, McLean, Fairfax City and Groveton. All have senior recreation centers and serve large midday meals to residents who prefer not to cook for themselves.

The county had plans for a fifth independent living facility in Herndon, but financing for the project was lost when a housing bond issue failed in this month's general election.

Arlington and Alexandria have not yet built independent living facilities, but private and religious organizations sponsor about 2,600 units in the close-in Northern Virginia suburbs, according to the 1990 Washington Metropolitan Guide to Retirement Living, which lists senior housing facilities.

The new guide will be published twice a year to keep up with the rapid changes in housing opportunities for seniors, said Publisher Steven D. Gerney. Complimentary copies of the first issue are available at area agencies on the aging.

Independent living rents in Northern Virginia range from $240 to $2,700 a month, depending on a facility's amenities and a resident's eligibility for subsidies. The most expensive are spacious units that include meals, laundry and housekeeping services, and even spas. The least expensive are compact efficiencies in subsidized projects.

In all price ranges, independent living facilities provide round-the-clock staff and allow tenants to control temperatures in their apartments. Most allow pets, with some limitations.

Most facilities do not offer care for frail people, but neither do they require the huge entrance fees typical of "continuing care" facilities.

Independent living facilities are much like other apartment buildings, with a few concessions to the needs of seniors: wide doors to accommodate wheelchairs, levers instead of knobs for arthritic fingers, tables stable enough to lean against when rising from a chair, and bright lights for weakened eyes.

Facilities typically have common areas -- lounges, game rooms, craft corners and libraries -- where residents are encouraged to socialize and stay involved.

People's reasons for choosing to leave their private homes are varied. Some suffer some loss of vitality, others feel vulnerable to crime or may no longer be up to caring for a lawn or driving on Northern Virginia's traffic-tangled roads.

"There's a very healthy, independent senior community in Fairfax County that does not want to worry about mowing the lawn," said Mary Stewart, spokesman for the county housing department.

Many are lonely, especially if they have lost a spouse or close friends. But typically they do not want to give up their independence by moving in with their children.

"They can get along on their own, but many do better in a supportive environment," said Carol Lifsey, who councils seniors and their families for the Fairfax County Community Services Board. "They read the paper, manage their own finances, but might not be able to cross Little River Turnpike."

Moylan's apartment is on a floor with 25 other self-contained units for healthy seniors, who share several lounges, a library and laundry facilities. The outside doors of the building are attended, and a staff member is on call round-the-clock.

Before moving into the Lincolnian, Moylan and her husband, who has Parkinson's disease, lived with her daughter in Springfield, a situation she said was uncomfortable for all of them.

"My husband and I felt homeless, without an address," she said. Moylan said she wasn't up to caring for all of her husband's needs. Today, he lives in another section of the Lincolnian for seniors who have health problems.

"We still live together and see each other every day," Moylan said. "I love this place. They're going to have to carry me out of here."

Some seniors have moved to the area to be close to their adult children.

"When you get older, you need to be near family," said Nardino, 68, a widow from New Jersey who moved last month into Fairfax County's 120-unit Little River Glen facility in Fairfax City to be near her son.

Nardino's compact, one-bedroom unit opens onto a courtyard with a fountain and shaded walkways that lead to the facility's main hall. She proudly shows off a space-saving ironing board that stows away on a closet door. Next year, she will plant flowers in her tiny yard.

"It's lovely here; so much more than I expected," she said with a sigh.

Still, Nardino admits, leaving her old home was exhausting and somewhat painful. "It was hard to move away from old friends and give up so many belongings," she said.

Residents usually go through an adjustment period, just as they would after a move earlier in their lives, said Sharron Dreyer, director of senior housing in Fairfax County. They concentrate first on what they've lost but soon get around to recognizing what they've gained, she said. "They say, 'Hey, this is my space.'"

"It worked out well for me," Nardino said. "I've already made several close friends here."