THE STUDENTS looked pensively out the windows of the bus. A sign at the foot of the mountains in Marblemount pointed up the isolation of the land and the extreme nature of the month ahead: 89 miles to the next tavern, it read. That's a long way between bars, even if you're not old enough to drink.

In this part of northern Washington, there's a chill in the air that doesn't register on thermometers. Winter is never far removed. It lurks in names like Freezeout Mountain, or the glaciers under Ragged Ridge. Two-thirds of all permanent ice in the Lower 48 states is found in the North Cascades.

The students drew their jackets close. They were high school and college teen-agers enrolled in a National Outdoor Leadership School wilderness course. The eight of them were headed for a month in the Pasayten Wilderness, a half-million-acre preserve along the Canadian border on the eastern slope of the North Cascades. Their leader was scarcely older than they, a 22-year-old woman trained by NOLS who grew up in the Washington, D.C., area but traded the debutante's life for mountains.

None of the teen-agers had met before the trip, but most had the same gift-wrapped background, growing up in wealthy eastern suburban families and attending private schools. They had spent past summers sipping Perrier at country clubs, touring Europe, catching Aerosmith in concert or working odd jobs or internships on Capitol Hill.

This was a summer of another sort, a month of footsore days and 70- pound packs. At times it would seem like boot camp with a twist. For the privilege of hiking themselves to exhaustion and sleeping in the noxious environment of a crowded mountain tent, they were paying $1,200 (tuition and food included).

But it would be more than the ache of the trail, the fear as they fought for balance in a fast-running creek. They would have the chance to form a society of their own making. As NOLS students, they would be guided by a set of values called Expedition Behavior that the school has shaped on the premise that the safety of a group depends on its cohesiveness. Ideal expedition behavior, in the words of the school, is "the whole orchestra playing together."

The students would appoint leaders, designate tasks and travel in small groups, reading maps and choosing routes. They would be free to make wrong turns--and to regain lost trails on their own.

THERE ARE SCORES of wilderness schools today with programs that range from rehabilitating juvenile delinquents to teaching teamwork to corporate executives (two intriguingly similar tasks). NOLS is one of the oldest, founded as a nonprofit organization in Lander, Wyo., in 1965 by mountaineer Paul Petzoldt. Since then it has opened branches in Kenya, Mexico, Washington state and Alaska and graduated more than 16,500 students from its courses.

NOLS' main purpose is "to teach people to live in harmony with the outdoors," says assistant director Charley Fiala. The school is in the forefront of the so-called "no-trace" camping movement. The number of back-country travelers has shot up like a Yosemite wall in the last 15 years, and many of them are wreaking discord, leaving garbage in mountain meadows, turning trails into hog wallows and building bonfires that wipe out an area's wood supply in a few minutes.

NOLS tries to teach people to trek in the spirit of martial arts disciples who cross the floor without tearing the rice paper. Students travel in small groups, and are admonished not to shout or wear loud clothes. "Wear earth colors whenever possible to minimize your visual impact," counsels the school's 10-page monograph on conservation practices.

The initiation begins with the school's basic "wilderness course." It's not a survival course, but a primer in how to avoid getting into a bind in the first place, short of staying home.

The education is not without risk. For every three NOLS courses, an average of two students are evacuated, mostly because of sprained ankles or twisted knees. Six students and one instructor have been killed in the school's history. A student on the wilderness course in the North Cascades once lost his footing on a steep trail. In a matter of seconds the instructors could tell the fall was fatal by the way the body bounced. In Wyoming, a student fording the Green River caught his foot in the boulders of the stream bed and died of hypothermia while rescue workers struggled to free him.

Students sign a release and are required to carry insurance. NOLS refuses applicants who are obese, have bad knees or are mentally disturbed. The last is a judgment call. One woman, asked if she had ever had any psychiatric care, wrote "maybe."

She was accepted.

The expedition I joined was known as NCW 6/7--NC for North Cascades, W for Wilderness and 6/7 for the day in June it set out. I joined the trip for the first "ration," a period of 12 days, rode out with the horse packer who brought in the second ration, and caught up with the trip again at the end of the third and final ration.

It was a sunny day when we crossed the crest of the Cascades in our bus and pitched down the eastern side into the valley of the Methow River. At Billy Goat Corral we stopped and stumbled out. We were 11 in all, uniformly dressed in earth colors. Whatever visual impact we had on the wilderness, it was having 10 times that on us. We squinted up at the blinding snowfields and black towers of Big Craggy Peak vaulting 4,000 feet above us.

At last, saying not much, we hoisted the packs and filed out, heading north for a place we'd never been.