Some of them seem to have everything: private schooling, cars for cruising their suburban neighborhoods, silver spoons tucked away since birth.

But America's middle- and upper-class youths are showing signs of startling unhappiness. They are fleeing their homes by the tens of thousands.

"I don't like to be told what to do," a 17-year-old Fairfax girl who was staying at Alternative House, a shelter for runaways near Tysons Corner, said last week. "I guess that's part of the problem."

The tall, well-dressed Fairfax girl spent several weeks at the home. This year an estimated 1,500 suburban Washington area teen-agers will spend at least one night in a local home for runaways.

Nationally, an estimated 1 million youths run away from home each year, and while no comprehensive figures separate these runaways by income level, counselors say that for every child escaping an impoverished, inner-city family, there is, at the very least, another running from an affluent suburban home.

Child protective professionals say that critical questions concerning runaway children have not yet been addressed by the current nationwide campaign to find them: who they are, where they go and why they suffer from more intractable problems than ever before.

The milk carton pictures, subway posters and television efforts to locate missing children center on the abducted child, counselors say, and ignore the problems of 98 percent of the missing -- those who leave voluntarily or are pushed out of their homes.

The problems of the 17-year-old Fairfax girl, whose father is an alcoholic and whose mother is separating from the girl's stepfather, are typical of runaways, said Robb Hasencamp, director of Alternative House.

"The runaways we're seeing today have far more complex problems and more of them," Hasencamp said. "One of the reasons is that the parents of the '60s never learned how to parent. They wanted to be kids' pals and thought the enlightened way was to let the kids do what they wanted."

Since the 1960s, when public attention first became heavily focused on runaways, the number of children under 18 who leave home without permission has remained almost constant. However, experts say that those numbers are misleading because there are fewer teen-agers today than in the '60s, meaning that the likelihood a child will run away has increased.

More worrisome than the numbers, though, are the reasons today's children are fleeing. Compared with the soul-searching youths of the '60s -- who left home to "find" themselves and to seek a less material, more peaceful world -- today's runaways are depressed children, often with multiple family problems: divorce, alcoholism, noncommunication, violence.

Even more than guarding against child abduction, counselors say parents now need to understand why young people are so discontent and distraught that they run from their past and plunge into a future that, in the worst cases, means prostitution, theft and drugs.

Estimates of the number of runaways in the Washington area range from 10,000 to 18,000 a year. Alice Benson, assistant director of the Alternative House, said that 4,000 of those runaways come from Fairfax.

Though the words are sometimes used interchangeably, strictly defined, a runaway -- a youth under 18 who leaves home without parental or caretakers' permission -- differs from a homeless youth, who leaves home with the mutual consent of his parents, because of an emergency situation or on authorities' orders.

June Bucy, director of the National Network of Runaways and Youth Services, said that many suburban children run to escape pressure from their parents' expectations, alcoholism, sexual and physical abuse, and the loneliness of living with seemingly uncaring, workaholic parents. Children of lower-income families also run from abuse and alcoholism, as well as the strains and guilt caused by constant penny-pinching, she said.

"They think nothing can be worse than what's going on at home," said Ward Sinclair, chief of the Department of Health and Human Services' New York Region Child Bureau. "But it is."

The mother of one Alexandria runaway who recently returned home said she is petrified her 13-year-old will slip out at night again. "We had recently moved and she fell in with the wrong crowd," the mother said, her palm pressed against her forehead as she recalled the problems of the last year.

"She learned how to shoplift and how to hot-wire a car," said the mother, who asked not to be named. "She'd sneak out of the house with another 13-year-old and they'd buy beer, and [have sex with] guys . . . . I wouldn't know where she was or when she'd come back. She is 13 years old and the worst thing about our family is I got divorced. This isn't supposed to happen to me."

One night the Alexandria mother learned her daughter and three other teen-agers were planning to run away and live in a nearby abandoned home. "It was humiliating. I ran after her telling her I loved her and finally they stopped . . . . I asked them why they were running away and one girl said when she told her mom she was leaving, her mother said, 'Go ahead. I'll help you pack. I'll put the luggage on the front lawn.' "

"That was the worst thing she could have done," said the Alexandria mother, who is currently enrolled in parent counseling classes. "Because, even if you don't mean it, you're telling your child you don't care."

In hindsight the mother, who is divorced from the girl's father, said she believes her child left home because she wanted attention.

"Divorce and single parenting are a large root of the problem," said Bucy, the national network director. In addition, Bucy attributed the deeply troubled runaways to today's highly mobile society that leaves children rootless and does not allow parents to easily leave their children with close relatives for weekend escapes. "Most kids have a pretty good reason for running away. People conjure up the idea of a runaway as a brat who got a Chevrolet instead of a Cadillac. That's not true."

Of the 50,354 youths who spent at least one night in one of the 210 shelters whose officials responded to a national runaway study released this month, fewer than half, 19,411, left voluntarily. The others left with the consent of their parents, or were "throwaways" forced to leave home.

"It's a great mystery why there is increased depression among youth," said Dr. Elliot S. Gershon, a psychiatrist at the National Institute of Mental Health. "You see it in the suicide rate, and in other studies. It's most striking among youths . . . . If the increase is such that it keeps up, depression could become even more of a major health problem."

A 15-year-old Arlington youth, who recently stayed at the Alternative House, said he felt depressed and "like I had nowhere to turn," when his mother kicked him out of the house after a fight.

The 15-year-old, who said he never knew his father, came to the shelter on the advice of his girlfriend, and after two weeks of counseling, he was preparing to return home. "It's not going to be easy. It's hard to change. But being here makes me realize I really love [my mother] and it's worth trying harder."