MELLY REULING'S students quickly hit upon the essence of their relationship with their course leader.

Whenever the weather turned bad, they wailed: "Melly!"

Whenever the way was treacherous, they bellowed: "Melly!"

Whenever they had to strike off on their own they would cry, "MEEELLLYYYY!!!" in a parody of helpless dependence that had an edge of truth.

At the National Outdoor Leadership school, the "course leader" is the equivalent of ship's captain, the all- powerful authority charged with the safety of the entire expedition. NCW 6/7 marked Reuling's first time at the helm.

At 22 scarcely older than her students, Reuling's role and expertise lent her a seniority beyond her years. Where they stood as greenhorns tangled in fishing line, with blistered feet and gear falling off their packs, she was a finished product of the NOLS program, trained in first aid and mountain rescue, a paragon of outdoor competence who could identify pussy toes and heart-leafed arnica, read maps, climb 5.9, set up Tyrolean traverses and truck up a mountain as if a 70-pound pack weighed no more than an evening purse. When Steve came down with a fever, Melly hiked out 15 miles alone in a blizzard to arrange the evacuation.

She achieves such feats despite the degenerated cartilage in her knees that requires her to eat six to eight aspirin a day to keep the swelling down.

Reuling grew up in the Washington, D.C., area, tramping the Blue Ridge with passages from Heidi in her head. Her father, a doctor at the National Institutes of Health, moved his family from Vienna, Va., to an 18th century stone manor house outside Winchester. There on the family's 375-acre farm, Reuling had the sort of life that went from the barn where she raised prize cattle to Tysons Corner, where she hit Bloomingdale's on weekly shopping trips with her mother.

But she was drawn more to the mountains than to the life of long driveways and expensive clothes. She took her first NOLS course when she was 16 and two years later skipped her debutante party to qualify as an instructor. Since then she has been working for the school in the summer and studying botany at Evergreen State College in Olympia, Wash.

A tall, stocky woman with thin blond hair and rock-hard triceps, Reuling has a deliberative air and a deep feeling for wilderness.

"I've always felt drawn to wilderness," she said one afternoon as we sat sipping licorice root tea. ". . . It has something to do with the simplicity, with spending time with people without the distraction. I've just felt intensely happy there."

Her sense of a "calling" in wilderness was not diminished even by the death of a close friend in a climbing accident. She can say philosophically that "you have to accept that death can be part of the wilderness."

As course leader Reuling carried a bureaucracy's worth of NOLS paperwork: evaluations, a trip log, campsite records, medical and evacuation forms, people- and animal-sighting report forms. She toted several pounds of lecture notes on climbing ethics, rope work, rainbow trout, group dynamics, first aid and comparative protein charts. She oversaw a small pharmacy containing--for emergency use only--Compazine, Tylenol with codeine, Percodan, Benadryl and injectable epinephrine. And she packed three quarters and a Visa card, in case she had to hike out and call for help.