A new Virginia law requiring students to stay in school until age 18 appears to be having little effect on local truants, according to school officials and students, but is adding to red tape.

"The law forces us to make efforts to keep those children in school," said Keith Burnett, assistant principal at Manassas Park High. But, he added, "truancy is far, far down the list of problems the courts are dealing with."

Youngsters who are truant and then return to school are most often spurred by their own ambitions, not laws, which are hard to enforce and are an ineffectual antidote to the complexities of truancy, say those who work with truants.

"I knew I wasn't going to get anywhere in life without an education," said Susie Rohrabacher, a Montclair 17-year-old who returned to Potomac High School this year after dropping out of 11th grade last spring. With night classes, she plans to finish high school in June.

If she had not gone back to school, Rohrabacher would have been truant until she turned 18 in March. She could have been taken to court, but filing the paperwork would have taken months, according to Prince William County truant officers. By the time anyone charged her, she would have long since turned 18.

To be a truant, a child must be registered at but not attending a school. The most recent figures that indicate the scope of truancy are from the previous academic year. In 1989-90, Prince William, with 41,000 students, had 3,000 reports of truancy and took 52 students to court. Arlington, with 14,000 students, had 352 reports and took 10 students to court. In Fairfax, with 129,000 students, there were fewer than 1,000 reports. Fairfax school officials could not say how many students were taken to court.

Truant officers have not compiled figures for this year that would show the effect of the new law, but Bob Nace, Prince William juvenile court intake officer, estimated that the new law, which took effect July 1, has increased his caseload by at least 20 percent.

This year Virginia increased its age to 18, becoming the eighth state to do so. Although several states have raised age requirements in recent years, 31, including Maryland, still end compulsory attendance at age 16, as does the District of Columbia. Ten require attendance until 17, and Mississippi lets students go at 14.

But many educators say that hanging on to students longer is little more than warehousing bodies.

"Just setting that age is not going to reduce dropouts. It's easy to change the law, but unless you change a lot of other things, it's not going to have a lot of benefit," said Chris Pipho, of the Education Commission of the States, in Denver. "If someone leaves, I don't know of any school that has time to look for them."

"It's awful hard to legislate people to do anything," said Joseph A. Spagnolo Jr., chief of the Virginia Department of Education. Spagnolo termed any age requirement "arbitrary" and said that the answer is to make school more attractive.

Virginia Del. V. Thomas Forehand Jr. (D-Chesapeake), a sponsor of the measure in the General Assembly, said that the law's purpose was to give schools an extra year to make education more palatable. "The idea is not to make these habitual truants and dropouts take chemistry and calculus, but to steer them to stay in school and learn a trade," he said.

But those who work with students with attendance problems see it differently.

"It's important that you keep trying, but there comes a point when there's not much more you can do," said Nancy Cook, the director of pupil services with Manassas city schools.

The roots of truancy are complex. One problem, many experts say, is that families today are not doing enough to keep youngsters in class. Attendance officers throughout the region point out that because more households have working parents, children often lack supervision.

But schools' efforts to be surrogate disciplinarians have not been successful.

"There's no family structure. It's very hard to discipline them when it doesn't come from the home," said Nancy Andrews, an attendance officer in Prince William for 24 years.

Schools in Northern Virginia try to deal with chronic truants in a variety of ways, such as giving them in-school suspension or taking away parking privileges. But such punishments mean little if youngsters aren't in school to get them. Habitual truants may be charged in court, where many get court-ordered counseling, probation or, in some cases, incarceration in a juvenile facility.

Many educators agree that truancy problems start early and that often, students are not really called to account for their attendance and grades until high school.

"If they get off on the wrong foot in ninth grade, they have trouble finishing," said Ray Anderson, principal of H-B Woodlawn, an alternative high school in Arlington. "They're moving from the middle school to a larger high school. Some need some assistance to make that transition."

It was in ninth grade that Joe Cook, 18, ran into trouble. A former truant and drug user, and now an alumnus of a juvenile facility, Cook is a senior at Woodbridge High School.

Although he could legally drop out of school at this point, Cook said he is determined to finish, keep up a B average, work at his after-school job and go on to community college next year. "I need to finish," said the strapping 6-foot-4 youth. "The {juvenile} home changed my way of thinking."