With more than 650 licensed day-care centers in the Washington area, choosing the right one can be a bewildering and emotional experience for parents.

It is a decision that will alter, however subtly, the kind of people their children will become because chances are their sons and daughters will spend more waking hours each week with teachers than with them. It is at the day-care center that many will learn to play, sing their ABCs and eat much of their daily bread.

There are public day-care centers and private ones, profit and nonprofit, many with names that read like the first line of a nursery rhyme. Some care for 20 children, others for 200, and the first step in distinguishing among them is to pay a visit and look around for yourself, child-care experts say. Any day-care center worth entrusting your child to should be willing to let you make a few unscheduled visits after your initial interview.

The expressions on the children's faces are one of the truest indicators that a center is keeping a child curious, cared for and well, but there are other things to watch for, too, the experts say:

* Safety. Look for safe, sanitary conditions, including a fire evacuation plan, fire extinguishers and well-lighted, sanitary sinks and toilets. They should be low enough for children to use easily.

If the center accepts children in diapers, are there adequate health precautions taken? First aid and emergency service should be available if necessary, and check to see that the center requires a medical report when a new child is admitted. The center should carry liability and accident insurance.

* Meals. Ask if the center serves a hot lunch and find out who plans and prepares the menu.

Because many children tend to eat little amounts at frequent intervals, a good day-care center will serve both a midmorning and midafternoon snack, which should be made from fruits, cheese and grain crackers rather than cookies and sweetened drinks.

Find out how the center keeps track of children's allergies and who administers medications.

* Equipment. On the playground, look for climbing bars, boxes, ladders as well as tricycles, wagons and swings.

Inside, check to see that there are natural materials, such as sand, clay, water and wood, to play with as well as a variety of wooden puzzles, pegboards and construction sets.

There should be at least one set of climbing bars indoors for rainy days, and there should be enough toys and tricycles so that children don't have to wait in line to use them.

* Staff. The adults who care for children are the most important element in determining quality child care. "It's really the personality and temperament and character of the day-care teacher that matters," one child psychologist said. Teacher training in early childhood education also has been found to be important.

Most day-care specialists recommend a ratio of no more than eight children to one teacher, and each overall play or class group should be no larger than 20; studies have shown the quality of care declines significantly in groups larger than that. Groups of children younger than 3 years old should be smaller.

Teachers should be warm and friendly and should treat children without sentimentality or favoritism. Look for low staff turnover, a sign of job satisfaction and a well-run center. Ask if there are provisions for staff sick leave so that teachers are not forced to come to work when ill.

Daily routine. The center should keep a schedule that balances indoor and outdoor activity and structured time with free play. For preschool day care, find out what emphasis the center places on certain skills. For example, are reading and writing stressed at the expense to the detriment of social skills?

Parental involvement. The center should show a willingness to keep parents informed of daily activities and encourage involvement with their children's care.

"You drop the child off at 7 a.m.," one day-care expert said, "and by the time you get back at 6, there's another shift of teachers. Will they know if she ate her breakfast, if she took her nap? That's important."

A good center will respect different family arrangements. Find out how the center keeps track of your child's development and look to see if reports to parents stress accomplishments as well as problems.

Once a child has been enrolled in a day-care center, experts stress the importance of watching for changes in behavior that might indicate problems. "Children are litmus paper," said Jerome Kagan, a specialist in early childhood development. "You drop a kid off and in the next 40 days that child will tell you whether day care is good or bad."

Kagan suggests looking for changes in eating or sleeping habits, disobedience or general mood. "If it's a big change," he said, "then it's probably the wrong center."

Further information on choosing a day-care center can be obtained by contacting local day-care councils or children's offices in county government offices.

Guidelines also are available from the National Association for the Education of Young Children, 1834 Connecticut Ave. NW, Washington, D.C. 20009; and the federal Administration for Children, Youth and Families, Head Start Bureau, Washington, D.C. 20201. Ask for the "Rainbow Series."