Margaret Denise is leaning back in her office chair and eating slices of cold chicken from a plastic bag. It's her lunch break and she's talking quickly. Denise kicks off her heels, pulls over a chair and puts her feet up. She points to a Marine Corps Marathon poster on the wall and explains she plans to train for the race this summer. She finished the marathon in 1978. This year, she hopes to run it faster.

For Margaret Denise, lack of energy is not a problem. At 49, with four grown children and two grandchildren, she works as one of 11 probation counselors with Arlington's Juvenile and Domestic Relations Court, meeting with troubled adolescents and their parents, investigating child custody cases and reporting to the county's two juvenile court judges.

Last month, when she was named Probation Counselor of the Year by the Virginia Juvenile Officers' Association, her colleagues were not surprised.

"She's believable and that's one thing I look for," said Judge Berton V. Kramer, who hired Denise in 1978. "Most of these kids are antiestablishment and it takes someone believable to instill in them some of the things they missed when they were growing up."

Her knack for coming across as genuine could have something to do with the kind of life experience -- rearing four children through adolescence, for instance -- Denise had before getting into juvenile court work 10 years ago.

"My feeling is, sometimes, life experience can be extremely valuable," said Carl Beyeler, director of court services for Arlington's juvenile court. "She's brought something to the job here that I don't always see."

As a high school senior in Washington during the 1950s, Denise had wanted to be a nun or a nurse. But after graduating from St. Cecilia's High School, she became engaged and worked as a stenographer for the CIA before getting married three years later. Over the next 10 years, she and her husband, a civilian employe with the military, had four children and moved 12 times.

In Hawaii, their last stop before returning to the Washington area, Denise started taking college courses at the University of Hawaii.

"I loved it," Denise said. "It really made me think for the first time."

Soon after moving to Northern Virginia in 1969, she enrolled part time at George Mason University, where she majored in psychology. The experience forced her to juggle child-raising and college.

"Sometimes it seemed the process never ended," she said. "Once four kids hit the door, you could never study."

But in 1976, she earned her degree and worked as an unpaid intern for the Fairfax County Juvenile and Domestic Relations Court for two years before accepting her current job. "I knew I wanted to do something with families and kids," Denise said. "I really like kids."

Denise said she enjoys adolescents. "They can be obnoxious and they can drive you to the brink. But they still have some freshness. They're not jaded adults yet. And you can see the possibilities."

"They're still reachable," she added. "They can be fun and they can be delightfully candid."

Denise is in charge of 23 probation cases, which make up a major part of her job. Most of the cases involve teen-agers who have been placed on probation by judges for such violations as drug abuse, larceny, robbery or theft. Her role is to refer the teen-agers to treatment programs when necessary and regularly meet with and counsel the teen-agers and their parents.

"I have lived and survived four teen-agers," Denise said. "I know how hard it is with adolescents because I've raised four. I think that probably carries some weight."

"I think being a good parent is the hardest job there is," she added. "It takes a tremendous amount of energy and patience. Nobody tells you how to be a good parent. You learn as you go along.

"The most consistent problem I see is that parents find it hard to accept that this young man or woman is a very separate individual," she said. "By the time they hit their teens, they're so questioning. Parents feel very threatened by this."

Although she loves her job, Denise admits it can be very tough, very stressful.

"You have to look at success in little increments," she said. "It's a lot like being a parent."

"Last year was really a bad year," she said, explaining that a teen-ager with whom she was working committed suicide and a child custody case she was handling developed into a murder.

Denise said the suicide was particularly upsetting. "I was really unable to work for a few weeks and I'd cry a few times a day," she said. "You do your soul searching -- was there anything else I could have done?"

Although her job brings frequent stress and occasional grief, Denise said she has no plans to quit.

"You have to pace yourself," she said. "I used to have the superwoman complex. You just learn to make some adjustments."