A HALF-DOZEN of them -- all novice cross-country skiers are wobbling in single file. They've just been released from a morning lesson and are free from the critical eye, and nagging voice, of the instructor. Free finally to glide on their own along the winding, woodland paths that skirt the base of a snowy mountain.

It seems they've got the hang of it; the basics don't take long to learn and, with some hesitation, they can tackle gentler terrain and make a few wide turns. But real mastery--and balance--require practice. Only minutes from the warming hut, this becomes evident.

"Oomph," exclaims a young woman as she suddenly topples from the hard-packed snow of the trail into the fluffy cushion of a deep drift. She is the first of many in the group who will tumble on this day, when class members learn well the art of regaining their feet--an act that isn't as easy as it looks with six-foot skis getting in the way.

A normally unathletic soul, the woman has been lured reluctantly into the wild outdoors by friends eager to try one of America's fastest-growing winter sports. All but buried rump-down in the snow, she brushes wet flakes from her face, looks up at the others gathering around her, shrugs her shoulders and bursts into rollicking laughter.

Add one more convert to the infectious fun of cross-country skiing.

Washington with its infrequent snowfall may not seem the logical place for a sport that depends on so much snow. But a drive just three to four hours to the west takes the skiing fan to the Allegheny Mountain valleys of Maryland, West Virginia and Pennsylvania which is blanketed with heavy snows--as much as 150 inches or more a year. A popular summer destination, these mountains are rapidly becoming a major mid-Atlantic winter sports center.

In spite of balmy winters, cross-country enthusiasts generally can count on good snow cover in the 2,000- to 4,000-foot elevations west of here from December into March and sometimes even early April. Then, a warming spring sun makes a day in the woods a special delight.

To cater to the region's surge in cross-country (as well as downhill) skiing, new lodging and trail facilities are continually being developed, mostly in or near state and national parks and forest lands; and at commercial ski-touring complexes that have sprung up near downhill resorts. (The sport is snaring many downhill skiers who have become discouraged by long weekend lines and hefty lift-ticket prices.)

Trail networks looping for miles are being built, many of them easily negotiated by beginners, and regularly scheduled classes are being offered. The trails are graded according to degree of difficulty and some are even being carefully groomed, the way alpine ski resorts maintain their slopes for better skiing.

To city dwellers, plunging into the winter woodlands may seem foolhardy when temperatures plummet unexpectedly and a sudden snow flurry can hide the way home. But at these supervised ski centers, it is difficult to go astray if basic precautions are taken--consulting a trail map if the area is unfamiliar, for example.

On moonlit nights, guides take small groups out to wander trails that sparkle like a ribbon of jewels in the reflected beams. And if the moon fails to peep, skiers put on miners hard hats and glide by the light shining from their foreheads. Both "eerie" and "magical," say participants, who add that it can also be darn cold to crawl out of a snowbank in the dark.

The sport's boosters worry that many people get the wrong idea about cross-country when they see grueling Olympic races on TV--endurance tests that leave the competitors gasping and viewers telling themselves, "Not for me." But recreational skiing is more like a walk through the woods at your own pace. If you don't want to hurry, you don't have to. And unlike downhill skiing, when you stumble, it's not at break-a-leg speed.

Over the past few years, three areas offering particularly good facilities have become popular for couples, families and group seeking a weekend skiing vacation. The idea is to combine the exuberance of a day outdoors with the apres-ski rewards of good food and comfortable lodging. You don't even have to search very hard to find a heated indoor swimming pool to soak tired muscles or a horse-drawn sleigh to transport you to lunch in style.

If you are a family, or even a couple, who is sharply divided between downhillers and cross-countryists, then the Canaan Valley-Davis area of West Virginia, about a 200-mile drive from Washington, may be just the spot to resolve the dispute. The area is on the verge of becoming a super resort with a number of condominiums and chalets on the drawing board. A friendly, down-home kind of place, the residents say, this part of West Virginia's Potomac Highlands claims to be one of the snowiest spots in the nation and one of the few areas east of the Rockies where deep powder snow can be found.

The locals describe the 14-mile-long Canaan Valley as "canoe-shaped." Relatively flat and open, it is surrounded by peaks reaching almost 4,300 feet and is the site of the 6,000-acre Canaan Valley Resort State Park, and the nearby Dolly Sods Wilderness Area. It is as close to the wilds as you will find anywhere near Washington. Davis, at the northern entrance to the valley, is one of West Virginia's first lumber towns and the state's highest (3,200 feet) incorporated community.

For downhill fans in the family, there soon will be three resorts from which to choose: the long-established Canaan Valley Resort; Mount Timberline which this year opened a couple of miles down the road; and Tory Mountain, located within 10 miles, which is scheduled to start up next year. The two new resorts plan major additions that will offer a full range of beginning-to-expert alpine skiing.

Meanwhile, new facilities for cross-country skiers have been keeping pace with a choice of at least four trail systems--totaling nearly 40 miles--all within 10 miles of each other. You can either venture out on your own with a trail map or follow a guide. Better skiers can even ski from one area to another and arrange for a shuttle pickup to carry them back to the starting point.

Newest on the scene is the White Grass Ski Touring Center (304-866-4114) that opened last year on 1,200 acres of farm and woodland in Canaan Valley. Years ago, the mountain rising up steeply behind the warming lodge and cafe was the site of one of the Washington area's earliest ski slopes called Weiss Knob. Now the mountain and surrounding flatlands are laced with 10 miles of groomed trails, open daily in season, with access to more skiing in Dolly Sods.

White Grass is operated by a group of young ski enthusiasts who have fallen in love with the outdoor life of West Virginia. In the past year, they have remodeled the old alpine hut, turning it into a cozy shelter where skiers can warm their feet by a wood stove while sniffing the aroma of home-cooked soups and baked desserts.

Area director Chip Chase, 29, a onetime forestry student in Richmond, is a former downhiller who gave up the fashion-plate atmosphere of alpine skiing for the rustic (and less expensive) pleasures of woodland treks on Nordic skis. He still gets some of the thrill of steep inclines, he says, by utilizing what is called the "telemark" turn, a technique taught at White Grass' daily morning and afternoon class sessions. Ski school head Winslow Ayer, 28, currently is the highest-ranking official of the Professional Ski Instructors of America in the south.

A second network of trails meanders for about 10 miles through the thick spruce and hemlock forests of Blackwater Falls State Park. Though the area is small, the density of the growth helps preserve the woodland serenity. "You never know there's another group just yards away," says Laird Knight of the touring center, also operated by White Grass. The facilities, open daily, include a warming hut, rentals and lessons.

The park is particularly scenic, with fine vistas of the Blackwater River canyon. Skiers can glide right down to the base of the frosty falls that gave the park its name. The sprawling Blackwater Lodge, about a mile away, offers comfortable rooms and meals. It fills fast on winter weekends.

Adjacent to the Canaan Valley Resort is a third network of about 18 miles of trails, also offering rentals and lessons. With 250 rooms, the new Canaan Valley Resort Lodge, a striking light wood structure of contemporary design, is probably the choicest of the accommodations in the valley. In all, the Canaan Valley-Davis area boasts about 2,000 rooms, from basic to deluxe, and on a winter weekend they can fill up.

From its headquarters in a weathered frame house on Davis' main street, TransMontane Outfitters leads groups, including beginners, along a number of other loop trails in the region, including one that passes along Canaan Heights with a spectacular view of the valley. A trip might last four to six hours, with lunch on the way at $35 per person, says instructor Alice Fleishman, a slight-framed 21-year-old in red bib overalls who doubles as the firm's head whitewater guide in the summer.

To the north in the Laurel Highlands of Pennsylvania in Somerset--and about 190 miles from Washington--is the Hidden Valley downhill and cross-country skiing complex, with a modern lodge, townhouse and chalet rentals and those special cold-weather delights: indoor pool, sauna and whirlpool. The ski-touring center is one of the largest in the state, with about 25 miles of trails winding through the thick woods that surround the downhill area. Rentals and lessons are available, and the trails are groomed. Spend Saturday on the slopes and Sunday in the woods.

A third popular (maybe over-popular) area is New Germany State Park in far western Maryland near Grantsville, about 170 miles from Washington. On a weekday, the six miles of trails within park borders (and additional miles in adjacent forestlands) may draw only 20 to 30 people. But on weekends after a snow, the crowds can swell to from 700 to 1,100 a day, says park manager Perry Edmiston. That's hardly the quiet woodlands, but the more-experienced skiers head out for the less-traveled forest paths. When the 13-acre lake freezes over, its flat surface adds more space to spread out.

There's a warming hut (the first skier who needs it builds a wood fire), and no lessons or rentals are available at the park. But River and Trail Outfitters of Knoxville, Md., now in its sixth season, schedules weekend excursions to New Germany. For $129 per person (you drive there on you own), you get two days of lessons and trail skiing, rentals, two nights at Casselman, an Amish inn, and five country-style meals from Saturday breakfast through Sunday lunch. (Similar trips are made to Blackwater Falls, with rooms at the Best Western Alpine Lodge in Davis for $139 per person, with access to the heated pool and jacuzzi.)

One caution: It can be snowing in the mountains even while the sun beams on Washington. The roads off the interstates are often winding and steep, so be prepared for hazardous driving conditions. A few weeks back, when the winter snow began in earnest, it didn't stop falling for days. Then again, there's always that dream of phoning in to the office snowbound when Monday is too early to end a weekend in a winter wonderland.