The statistics are alarming: Some 3 million American children aged 6 to 13 return home from school to empty houses. Something like 50,000 children under the age of 6 are left home alone for most of the day.

These are the "latchkey" children, so named because they often carry their own house keys to let themselves in while their parents are at work. Children fending for themselves--in many cases because their parents cannot find, nor afford, adequate day care--is a phenomenon of increasing disturbance to parents, educators and child-welfare experts.

"Most of the children seem to be from families trying to make the best of a bad situation," says Catholic University Prof. of Counselor Education Tom Long. He and his wife Lynette Long, 34, assistant professor of education at Loyola College, Baltimore, are writing a book on latchkey children. The figures they provided above, they say are conservative estimates and when school is out, it is expected that more children will be on their own for longer periods.

"The parents express a lot of guilt," says Long, 43. "They are anxious. They have what employers call the 3 o'clock syndrome--worrying and looking at the clock. They know the situation isn't the best for the kids."

Although the term has become pejorative, "latchkey" children, as the Longs point out, are not necessarily symbols of neglect. It is the thought of a 5-year-old fending for himself that they and others find disturbing, not of a mature 13-year-old spending two hours a day unsupervised, with adults nearby to call for help.

Professionals disagree about the age and in what circumstances a child can be left alone, but most share Lynette Long's recommendation, "Not too young, not too much responsibility, not too long, and not isolated."

Most jurisdictions let local agencies determine the age and other factors which constitute "parental neglect." D.C. area child-welfare agencies' minimum recommended age for leaving a child alone ranges from 10 to 13.

When the Longs interviewed 300 area latchkey children--"from very poor to very wealthy" in Northwest and Northeast D.C. and southern Montgomery county--they found that "loneliness and fear are the children's two biggest problems".

One-third of the children experience "severe" fear which they did not tell their parents about, and at times suffer recurring sleep disturbances. Some children said they lock themselves in the closet, bathroom or shower until someone comes home. Children alone, as the Longs note, are vulnerable to obscene phone calls, molestation and other crimes, inablity to handle emergencies.

Although family-service agencies are trying to mitigate latchkey problems by providing more day care, the supply is still inadequate. In addition, programs often are too expensive for working families, especially single parents and those with several children. A closing time of 6 p.m. is not always convenient.

Even when quality, affordable day care is available, children at age 11 or so either become ineligible or begin to balk at having a "baby sitter." Working families face those awkward years--with anxiety and little assistance--when children are too old for baby sitters but not ready for day-to-day responsibilites.

To help bridge this gap, a grassroots movement is emerging to help prepare children for being alone. Books on survival skills for youngsters are beginning to appear. (The Longs' next book will be a handbook for parents on teaching children how to take care of themselves.)

Among community-service agencies that have stepped in to prepare children for being alone: the Alexandria Cooperative Extension Service; the Mental Health Department of Johnson City, Kans.; the Minneapolis Red Cross; the YMCA in Portland, Ore., and the Norwood Avenue School in Cranston, R.I. Their innovative programs teach basic skills in cooking, housecleaning, home-safety, emergency techniques; some are addressing the more intangible problems of fear and loneliness.

"Survival Skills for Kids," a course designed by Nancy Pfafflin of the Alexandria Cooperative Extension Service, is geared to children 8 to 13.

"The skills involved in the course are useful, for almost every child over the age of 8 is left alone for a few minutes," says Pfafflin. "With 65.5 percent of the mothers of 6- to 17-year-olds working, children are often left alone for long periods of time at an earlier age.

"The goal is to teach the children to be cautious and responsible without creating undue anxiety. The course is upbeat and constructive; therefore, the children don't build fears, they build confidence in their ability to cope. Children are urged to discuss the learned skills, ideas and techniques with their parents."

"Survival Skills" has been taught in Alexandria community centers and is being given to students at the Alexandria Community Y (ACY) extended day-care program at the James K. Polk Elementary School. More sessions are planned at day-care centers, at summer recreation programs and on request.

The Alexandria Extension Service also may develop a parents' class on survival skills for children.

"Survival Skills for Kids" is taught in six two-hour sessions. Through role-playing and other hands-on techniques, the children learn how to use knives safely, call for emergency help, persuade peer guests to comply with house rules, apply first aid, perform emergency procedures (such as the Heimlich maneuver to save choking victims), to deal with loneliness and boredom, talk on the phone and for the grand finale: prepare and serve a meal.

A paramedic and a policeman address the group about safety and emergencies, with an emphasis on identifying those that require outside help.

Derek Drake, a 6-year-old student at ACY's Polk program, proudly ticks off the things he learned in the first three of the six sessions: "How to take care of ourselves, how to save a life--to help people choking or not breathing, not to leave the pot handles out, not to climb on counters, not to play with matches, not to put something on a chair and stand on it, not to bounce things in the living room, not to touch a gun in someone's house and not to lean on windows.

"We learned how to convince people who try to get information on the telephone . . . to talk firmly, not say 'uh, uh,' and we had fun learning how to prepare a snack for our family or friends."

What does he think about all this new, grown-up information? "I like it. That way my mother can trust me and I won't have to get scared."

Derek's mother, Paula Drake, 30, a vice-president of a computer-supply firm, is equally enthusiastic.

"He's been educating me. I think the program is excellent and they should have it in all the schools." Even children like Derek--"who is never left home alone"--can benefit, she says. "Sometimes if it's said outside the home, kids listen more."

"Survival-skills classes are very worthwhile because kids left alone are totally unprepared," says Tom Long. "All kids, regardless of whether they are latchkey kids, should have them."

However, he warns, "There is a press on for kids to be adults. We think, if we give them skills, they can activate the skills like an adult. That's not true."

Karen Berman, director of Alexandria ACY's extended day care, says she is offering the survival-skills class to prepare the children for "normal growth toward responsible independence," but also because she knows that many young children often are responsible for themselves.

When a cut in federal funding last fall required the 5-year-old ACY extended day-care program to raise the fees it charges its lowest income families from $3 dollars a month to $40 a month, a third of the children dropped out. This summer, the same funding cut will force the closing of one of ACY's summer day camps.

Because of frantic calls from many of the parents, Berman fears that some of the families will have no alternative but to leave the children alone. Thus, at the Polk program, children from 5 to 7 also are participating in the survival-skills class. Because younger children typically are not ready for such independence, however, they have not responded as well--with the exception of Derek Drake--as those 8 and older.

"With the 8-year-olds and up, we've had very good response from the children and the parents," says Pfafflin.

"At an earlier session which I taught in a community center, several 13-year-old boys came. They were teased about it by some of the children outside, but they stuck with it. At the end they told me they were disappointed it was over. That's the best compliment we could get."