For many Virginia parents, the availability of quality child care is the difference between working or not working.

"I spent weeks looking at day care centers, interviewing babysitters, checking on family day care homes. When I found a center I felt good about, I reserved a slot and then I started job hunting," said an Arlington woman who decided to go to work when her son turned 3.

"If I hadn't found a good situation, I wouldn't have looked for a job," she said.

The number of working mothers with children under 6 has tripled since 1950. Thirty-seven per cent of all mothers with children under 6 and 45 per cent of mothers with children under 18 are gainfully employed, according to a survey made last year by the Bureau of Labor Statistics.

Neither the quantity nor the quality of available child care has kept pace with the need. With families scattered, the working mother's mother is rarely available to help out. Fewer women are applying for jobs as housekeepers, and the rapid growth of day care centers in the 1960s has tapered off because of decreased federal financial support.

Despite the difficulties, it is possible to find satisfactory and dependable care. As a service to working mothers and their families, the Virginia Weekly has compiled this guide to child care in Alexandria, Fairfax and Arlington.

Parents can expect to pay about $40 per week for a full day of care in a center. Federal subsidies through Titiel 20 of the Social Security Act are available to parents who meet income eligibility requirements - around $7,000 for a family of four. Fairfax and Arlington have subsidy programs on a sliding scale basis for parents who are over the federal income eligibility level but who still need financial aid. Who Can Help

In Fairfax County, the Office for Children (691-3175) publishes a directory of licensed day care centers, a list, of extended care centers, which are after-school programs, and a limited list of family day care homes, where women care for children in their homes. Several booklets on how to choose a facility are available.

The Department of Social Services (938-5300) can help parents eligible for child care subsidies through Title 20 of the Social Security Act. Parents who want to determin whether they are eligible for county subsidies should call the Office of Children.

In Arlington, the Child Care Office in the Department of Human Resources (558-2234) publishes a directory of licensed day care centers and a booklet on how to choose a facility. They will soon have a list of licensed day care homes. Information on after-school programs is available through Pat Rowland (558-2884), coordinator of the program for the Arlington public schools. Parents eligible for subsidies for child care should call the Social Services Department (558-2892).

In Alexandria, the day care coordinator for the Department of Social Services (549-7707, ext. 251) provides a list of licensed day care centers and information on two after-school programs available in the city. Parents eligible for federal subsidies for child care should call the same number.

THe regional office of the state Department of Welfare (241-1880) maintains a list of licensed family day care homes in Northern Virginia. Day Care Centers

In Virginia, a day care center is a facility caring for 10 or more children all or part of the day. Most provide care for youngsters 2 through school age, although some centers are attempting to develop infant-care programs.

Child care specialists agree that at its best, a day care center can provide young children, especially those aged 3 to 5, with the benefits of intellectual stimulation and socialization.

"Day care fills a need for parents who cannot be with young children throughout the day, but it should also fill the needs the young children have. Some day care is custodial with a kind, loving atmosphere, so it's a safe, sound place to stay. Other programs have a strong educational component in combine, is ideal," said Nancy Clough, director of the Gerard Majella Child Care Center at Marymount College.

Child care specialists define a good center as one that has teachers and aides who have backgrounds in early childhood development, a low ratio of children to staff a variety of attractive equipment, areas suited to different activities, a plan to keep the day varied and stimulating but comfortable, and a program that invites parental participation in planning, activities and child development seminars.

"Everyone hears about the housekeeper who's a gem, but my experience in working with parents in Fairfax County is that they have been happier and experienced less turnover with day care centers than with housekeepers," said Judith Rosen, director of the Office for Children. "The quality of day care in the area is uneven, though. Some of our centers are providing excellent, top quality care, some meet only minimum standards."

While each center must be judged individually, observers of day care agree that one of the most important factors in providing good care is the child-to-adult ratio.

"Children are at a center all day long and need individual, adult attention. A lower ratio makes this more possible," said Elizabeth Hazel, Arlington's child care coordinator.

Centers with social service or vendor contracts (centers authorized to accept children who receive federal subsidies) often provide the best care because they meet stricter federal requirements for child-to-adult ratios, according to child care experts.

While regulations vary with age groups, federal requirements average one adult supervisor for every five children; state licensing requires 1-to-8 for 3-year-olds, and 1-to-10 for 4-to-5- years olds. The Department of Health, Education and Welfare is rewritint the federal requirements on staffing and expects to have the new regulations completed by October. In the meantime it is unclear whether centers can be required to abide by the former standards, said a local official.

"We are trying to hold the centers to the old requirements until the new ones come out," said Jane Ingrist, day care coordinator for Alexandria.

Regardless of how they are organized, day care centers cannot operate legally without a license, issued annually by Virginia's Department of Welfare. In Arlington, they also must have a county license.

State licensing specialists from the regional office in Falls Church and county health, environment and fire officials inspect the centers. State inspectors make at least one announced and one unannounced visit a year. Licensing requirements encompass fire, safety, staff ratios, and health requirements for staff and children. The director of a center must have 15 hours of college credits; teachers must have high school diplomas or their equivalent; aides must be able to read and write. Centers must provide personnel with the opportunity for training and verify participation.

"While our licensing standards are minimal, you can't confuse this with quality of care standards," said Rosen. "A license is the floor below which the community doesn't think good care can be rendered. It doesn't speak to the marvelous things that can be done for children."

Arlington County standards are higher than state standards in regard to staff training and education, adult-to-child ratios and program planning. A counselor from Arlington's Child Care Office inspects facilities three to four times a year. How to Choose a Center

Once parents have located a licensed center offering the hours and services they require, how do they assess the quality of care?

"They should pay an in-person visit and observe the children: Are they at ease with adults, with their peers?" suggested Rosen. "Look into the training of the staff and watch them work. Are they providing too much or too little guidance? See if the space is uncluttered. Are there many things to do? Check out the art supplies, books, range of toys. Remember a license is only a ticket to operate and should not be seen as a goal or objective."

"Parents need to be educated to be sophisticated observors of the room," said Mary Thorman, former director of the Gerard Majella Child Care Center at Marymount College. "They should look to see if materials are available for children to play with by themselves so that there's a minimum dependence on adults. On the playground, children should be able to go from one apparatus to another without asking permission. Room arrangement plays a crucial role. One large room without dividers lends itself to children running around rather than going into quiet areas to work."

Communication between center and parents is also important. Several centers have developed programs that include parents in various activities and offer them forums on aspects of child rearing. After School Care

After-school or extended day, a form of day care keyed to school age children and often located at elementary schools, is growing quickly in Northern Virginia.

Arlington had three extended care programs serving 66 children in 1969; by September there will be 21 programs serving more than a thousand children. Fairfax started three centers three years ago and now has 12 Alexandria has two.

After-school programs at schools are not licensed as day care centers. They are run by the public schools and, in the summer, by the departments of recreation. The program fills what was a need for inexpensive but stimulating supervision of school-age children.

Fees vary from program to program and are based on cost. Sliding scale fees based on income are often available. Some provide before-school care as well.

Since many of the programs are located at existing schools, they may not remain open on school holidays or when schools is closed because of bad weather. Another problem is setting up a program flexible enough to allow older children to attend Cub Scouts or group piano or other activities offered at the school or in the neighborhood.

Before deciding on an after school program, parents should check the activities. It is not always easy for a child who has spent the day in school to continue with a heavily structured program.

The same atmosphere and warmth a parent looks for in a day care center should be apparent in the after-school program. Guide to Day Care Centers

In compiling this guide to day care centers, the Virginia Weekly surveyed the licensed centers in Fairfax, Arlington and Alexandria by mail and telephone. The listing that begins on this page is of the 84-full-day, year-round centers that responded to our survey. Information on fees, hours and services was provided by the centers.

For a complete list of centers, including seasonal and part-time facilities, call the State Department of Welfare, regional office, 241-1880; or the Office for Children in Fairfax, 691-3175; the Child Care Office in Arlington, 558-2234; the Department of Social Services in Alexandria, 549-7707.

For a list of centers in the District of Columbia call the Department of Human Resources, licensing and certification division, at 629-5846. For Montgomery County centers call the health department at 279-1997 or Four C's at 279-1773. In Prince George's County, a list of centers can be seen and copied at the health department. Department employees will give names of centers in a specific area over the telephone; call 794-6660.

Next week, the Virginia Weekly will discuss other types of child care and how to find them.