The girl, her dental braces gleaming in the camera lights, said she was 16 years old and that she had tried to kill herself three times. She was, she said, "flawed" by poor health.

"The first day I cut my wrists with a knife. Each day afterwards for a week I cut them deeper. The last day I took some pills," she told a Senate subcommittee yesterday. The pills were her last effort at self-destruction; she had slit her wrist when she was 13 and later starved her 5-foot-5 frame to 70 pounds.

Yesterday, a year after she spent six weeks in a Northern Virginia psychiatric hospital, the Washington area teen-ager who asked to be known as "Julie Smith" was cited as an example of how local officials can reverse what some witnesses called an alarming national increase in teen-age suicides. A Fairfax County program that instructs every high school teacher on the early signs of suicide was credited with reducing the number of student suicides from an estimated 20 in the 1980-81 school year to three last year.

That drop occurred in the same year that 5,000 adolescents across the nation killed themselves, making suicide the second leading cause of death among 15-to-24-year-olds, said Alan Berman, president of the Washington-based American Assocation of Suicidology. "Most did not want to die, but knew no other way" to cope with their problems, he said.

Sen. Arlen Specter (R-Pa.) agreed that suicide was "one of the biggest problems" that student confront and said he called the hearing before his Judiciary subcommittee on juvenile justice to get a "first look at how the federal government might tackle this growing problem."

The panel got a lot of suggestions on that point. "Smith" told the senators that she now realizes that her health problems -- spinal curvature, kidney problems and migraine headaches -- should not be ended by suicide, which she said was "glamorized by TV." Her advice was direct. "No matter how bad things may seem, they will get better," she said in a low and even voice. "I would tell all teen-agers to 'hold on.' "

Marcia and Robert Scherago, a Northern Virginia couple, told of their horror at discovering the body of their 16-year-old son hanging from a back yard tree, a rope firmly around his neck. A few weeks earlier, "He asked me if I ever considered suicide," said Marcia Scherago, now a social worker who counsels parents whose children have killed themselves. "I took it lightly. I thought it was a normal question for a teen-ager to ask."

She advises parents to raise the question of suicide. "It's like sex. If we don't talk about it, the kids won't know about it. You know that's not true. It leads to more trouble."

"It's shocking and upsetting that young people don't want to live," testified Myra Herbert, head of the suicide prevention program in Fairfax, which Specter called a model for the nation. "But the best thing that we can do is create an awareness of the problem." In Fairfax, psychologists and counselors are available to all students.

Herbert said the leading cause of teen-age suicide in Fairfax is the "the confusion of students when they realize that they can't meet their parents' expectations -- voiced or unvoiced -- to do better than they." She also said that the county's high divorce and mobility rates contributed to student suicide.

Estimating that "well over 40 percent" of the Fairfax's 124,000 public school students have divorced parents. Herbert said too many people "only associate suicide with alcohol and drugs."

Berman, a psychology professor at American University, warned parents not to underestimate the problems their children face. Poor grades and the loss of a girlfriend or boyfriend can be "very disruptive to students," he said. Parents should be sensitive to signs of withdrawal, hostility, and "above all ask questions," he said. "It's mythical advice to keep your mouth shut."

Specter appeared to be moved by "Smith's" testimony and thanked her for speaking. Her mother also testified. "Listen, observe, get involved," she advised parents. "Sometimes you might step on toes, but you can't get too involved." She said children today were crying out for parental involvement. Her daughter took her arm and nodded.