Susan Thornton was tired of her 16-year-old son's hassles with the law. She was disgusted with his drug habit: Once she found a packet of cocaine hidden in the family encyclopedia. She was fed up with the calls from the principal saying her son had been kicked out of school--again.

And she was sick of worrying every time he ran away from home. Early this summer, he did it again.

"I went through five days of anguish not knowing where he was," Thornton said recently, her voice choking.

When her son finally came home, he spent two days behind bars in a Fairfax County juvenile detention center.

"I put him there," the 38-year-old divorced mother said. "Because of me, my son is up on two felonies: taking the family car without authorization and violation of probation."

That was June 29. "It was the first peaceful night I'd had in years."

For Thornton, there were no regrets. No remorse. No guilt.

"He ruled the roost until he split the whole family apart," she said, asking that her son's name not be used. "He was tearing out my insides. I have another child, a job to go to. I couldn't let him ruin that anymore."

A Fairfax County juvenile court judge placed Thornton's son at Elk Hill Farms, a school for delinquent boys about 50 miles west of Richmond.

He has lived at Elk Hill Farms for the past six weeks, and if Thornton has her way, he won't return home to the same mother.

"I was a marshmallow," she said. "I was never tough with this child. He walked all over me."

Thornton is taking lessons in getting tough with her son, preparing for his return.

She has helped organize an Annandale chapter of Toughlove, a national movement designed to teach troubled parents to stand up to their problem children. Toughlove is to some parents what Alcoholics Anonymous is to alcoholics, and Overeaters Anonymous is to compulsive eaters, according to one father who sought support from the group.

"Parents are the last group to be helped," he complained at a recent meeting of the Annandale chapter.

One of the main tenets of Toughlove is that parents too often are victimized by a child-centered society. And despite all the psychologists and self-help books that advocate Tender Loving Care, it just doesn't work with some youngsters, Toughlove advocates say -- especially those who are in trouble frequently.

For those kids, Toughlove organizers say, parents need to get tough: Lock the youngsters out of the house if they refuse to follow family rules. Take away their allowance. Take away the car keys. Don't bail them out of jail when they get in trouble with the law.

Parents need to learn to say "no," Toughlove goals state. To set bottom lines. To face up to their child's problems.

"We are not advising you to stop loving or caring about your teen-ager," Toughlove founders David and Phyllis York wrote in their self-help manual for parents. "But we are suggesting that you stop treating your young person like a poor, helpless child."

The Yorks, family counselors in Lansdale, Pa., established the first Toughlove chapter almost five years ago after police arrived at their home, carrying shotguns and an arrest warrant for their 18-year-old daughter, who had been charged with robbing a cocaine dealer.

"It was like a television scenario of a big drug raid," David York said in a telephone interview last week. "There I was, standing in my shorts with seven policemen holding their loaded shotguns on me.

"We were dismayed and frightened. We had listened to the psychologists, we had gone to family counseling, we had tried to work with the schools."

They decided all the therapy was worthless. "What we needed was other folks coming in and being supportive," said York.

In the five years since Toughlove was founded, the movement has spread to almost 200 chapters throughout the United States and Canada, including Falls Church, Annandale, Virginia Beach, Hampton, Staunton and Newport News.

Taking a hard-line approach to their kids' problems seems to be one of the main attractions of Toughlove.

Many of the parents who turn to Toughlove admit they are scared, bitter and frustrated. They have spent hundreds of dollars for counseling services and court fines. They are emotional wrecks. They think this may be a last resort.

"People don't want to face up to their teen-agers' problems," said Mary Ann Multer, a divorced mother of three older children, who is helping organize the Annandale Toughlove group. "It's acceptable to discuss problems when your kids are young. But when they get to be teen-agers, you don't want to talk about it -- it's embarrassing."

And there are no easy answers. A sampling of some of the problems faced by parents at recent Toughlove meetings in Northern Virginia tells the story:

A school counselor admits her daughter is a "bum," a high school dropout who locks herself in her bedroom, emerging only to yell and curse at her parents.

A successful businesswoman says her teen-aged daughter has been a drug addict and alchoholic since age 13.

The wife of a wealthy lawyer searches for ways to cope with a 17-year-old daughter who sleeps with her boyfriend in the family basement.

"It feels rotten to know you failed as a parent," Susan Thornton admitted during a Toughlove session last week in Annandale. "There are parents like us all over the place, we're just in hiding."

At each Toughlove session, parents pour out their grief. They take turns sifting through the emotional debris of the other troubled parents. And for what may be the first time, they feel like someone is on their side.

It's okay to admit your child is a bum, a hellion, a con artist. The others understand.

"How long can you take it?" asked one mother whose 18-year-old daughter has had a recurring drug problem and recently had an abortion.

"You have to reach a point when you care about yourself more than that 18-year-old who's made your life miserable," responded another distraught mother of two teen-agers.

The parents begin by sharing their troubles; they end each session trading solutions to the problems.

For example, one mother got fed up with begging her daughter to wash the dishes.

"I gathered up the dirty pots and dishes from the kitchen and put them on top of her bed, her clean clothes, her dresser -- soapy water and all," said the mother, a well-to-do businesswoman. The result: Her daughter now washes the dishes without prodding from her mother.

The other parents snickered with glee. They clapped. "I love it," shrieked one.

The parents are quick to form bonds and offer support. At the first meeting of the Falls Church chapter last week, one woman complained that her teen-ager and his friends sneak home from school every lunch hour to drink beer and smoke pot. Since she works, she can't be home to patrol the house, which is only a few blocks from the high school.

Other parents immediately volunteered to stop by her house each day at noon. Problem solved, at least temporarily. The parents will monitor the problem at the group's weekly meetings.

The solutions don't always work, and the Toughlove approach may not win support from all quarters, especially from psychologists and counselors concerned that a "too-tough" attitude and a failure to admit the parents' role in the youngsters' problems can simply mask problems without searching for the deeper cause, and hopefully a cure. But the parents who come to Toughlove say they have talked all they can, and now is the time for action.

With the help of others, they say, they may have taken what they consider the first real step toward resolving the agony besetting their children and their family. And if one problem child can't be helped, perhaps they can prevent problems with their other children.

"Toughlove can't change the kids' behavior," said Multer. "But you, the parent, can change yours. You can make sure your kids can no longer push the right buttons to make you feel guilty for standing up to them."

Two Toughlove groups have been formed recently in Northern Virginia.

The Annandale group meets at 8 p.m. each Wednesday at St. Matthew's United Methodist Church, 8617 Little River Turnpike, Annandale.

The Falls Church group meets at 7:30 p.m. each Tuesday in an office at 100 W. Jefferson St., Falls Church.

For more information on both groups, call Mel Riddile, coordinator of substance abuse prevention for the Fairfax County Public Schools, at 698-7546.