THERE WAS a time when the quiet and steady fall of wispy snowflakes heralded the new ski season. Nowadays, snow guns, blasting out their frosty blizzards with a clamorous whoosh, have superseded nature in blanketing Washington area mountain slopes.

As noisy and unsightly as they are, these snow-making devices are essential to skiing in the mid-Atlantic -- dubbed the "Banana Belt" because it lacks such skiing basics as alpine peaks, consistently cold weather and heavy snows. Without the machines, the local ski industry would still be where it was only two decades go. And that was practically nowhere.

With the help of snow guns, the ski business here has grown tremendously, each season offering new trails, more lifts, better accommodations and even a taste of the apres-ski nightlife that makes Aspen and Stowe dazzle. The upcoming winter is no different, with several winter resorts reporting million-dollar additions completed this fall.

What has happened over the years is that this fledgling industry, after a period of youthful growth, now appears to be entering its maturity, where it is offering a full range of skiing experiences. Vacationers -- especially those who want to spare themselves air fare to the Rockies or an all-day drive north to New England -- might consider a week at one of the larger local resorts, something hardly imaginable a decade ago.

Over the years, at least 20 ski areas have sprung up within 260 miles of Washington in Virginia, West Virginia, Maryland and Pennsylvania. Most expect to open between now and mid-December (some may already be operating) for a season that can extend through March and sometimes into April. The Washington area is now home to an estimated 330,000 skiers, with at least a half-dozen active ski clubs, including one of the nation's largest, the Ski Club of Washington, D.C.

One sign that the local skiing industry is growing up fast is the fact that several resorts -- particularly Wintergreen in Virginia and Jack Frost and Elk in Pennsylvania -- are opening new trails this season designed especially for advanced and expert skiers, who have had to travel to distant mountain ranges for downhill thrills. (Ski Liberty, near Gettysburg, opened four intermediate-advanced trails and a quadruple-chair lift last year.)

In the past, the bulk of Washington's native-bred skiers tended to be beginners and intermediates who had no need of steep runs. For the good of their bones, they were better off on the gentler trails that predominated in most local resorts. But with lessons and practice, they have graduated to bigger challenges--the heart-catching bumps and twists and plunges provided by expert runs. On these precipitous inclines, the reward is red-cheeked exhilaration. It's what makes the sport so popular.

Back in the early days, Washington skiing usually meant a day trip or at best an overnight stay in a highway motel. Hardly a match for a romantic mountainside chalet in the Alps, and not likely to keep a skier around for a week's vacation. Since then, construction of A-frames, condos and lodges has boomed, and with them the amenities of apres-ski: saunas, hot tubs, heated pools, a choice of restaurants, bars with live music and dancing.

Skiers can now find a night scene comfortable and lively enough to lure them to stay for several days. These are the vacationers that Snowshoe in West Virginia, the region's largest resort, is aiming for. Snowshoe reports adding 700 more condominium rooms over the summer, which means it can now put up 6,000 guests a night. They also added a "Top of the World" shopping mall, a conference center and several dining spots, bringing the total number of restaurants to 12, not including slopeside lunch stands.

One more example of how far the local industry has progressed: By next year, skiers heading for Canaan Valley near Davis, W. Va., should have a choice of three resorts within less than a dozen miles of each other. That's the kind of concentration you find in New England.

A new resort, Mount Timberline, is opening this year near the existing Canaan Valley area. For the time being, at least, both are concentrating on the beginning-to-intermediate skier and "family" skiing.

By next November, a third resort, Tory Mountain, is expected to open, initially with 10 to 12 trails ranging from beginner to advanced and with three triple-chair lifts. In a region of West Virginia's highest peaks, most of the trails will be 4,000 to 4,500 feet long. Subsequent development calls for the addition of the Seneca Bowl for experts, with 1,500 feet of vertical skiing and a 60-percent downhill pitch. ("Vertical" is an often-cited statistic, measuring not the length of a trail but the difference in altitude from the top to the bottom. Around here, where verticals begin at about 400 feet, a 1,500 vertical is the big time, approaching the 1,500-to-3,000 figures of Vermont's major mountains.)

The Tory people also have a second mountain, Brierpatch, to build on within their 1,500-acre holdings. The vertical there, they say, approaches 2,000 feet, with the possiblity of trails up to two miles long.

For the moment, the three areas see themselves not as competitors but as cooperating attractions to draw more attention to West Virginia skiing. Canaan Valley resort already is promoting a tri-resort winter vacation that includes sleigh rides, horseback rides and cross-country skiing at White Grass Ski Touring Center.

Beyond this, what else is new this season?

One thing that isn't -- at some resorts -- is the lift price, which remains the same as last year at Pennsylvania's Blue Knob ($18, weekend adult ticket) and Seven Springs ($17); Virginia's Bryce ($20) and Massanutten ($20); and West Virginia's Alpine Lake ($11, open Friday and weekends only). The gloomy economy is given the credit for the hold on increases.

Elsewhere, ticket prices are going up from 50 cents (Wisp at Oakland, Md.) to $2 per adult ticket, with the top per-day weekend rate reaching $24 (for skiers not lodging on the mountain) at Snowshoe. Cheaper rates are offered in a variety of ways: weekdays, early season, late season, children's tickets, learn-to-ski packages and half-day, night and twilight skiing. (The cheapest ticket is one day of free skiing, Friday, Nov. 26, at Hidden Valley in Pennsylvania to inaugurate two new triple-chair lifts, a remodeled restaurant and a new conference center. That's if the weather is cold enough to make snow by then.)

The cost of accommodations varies, with a rule-of-thumb that the closer you are to the mountain the more you will pay. Weekends and holidays are most expensive. At Virginia's classy Homestead in Hot Springs, the daily rate for a twin room begins at $82 per person, including three meals. Wintergreen's two-day "Come-to-Ski" weekend package begins at $140 per person for a couple in a studio apartment, including lift tickets. Snowshoe estimates lodging and ticket costs at $50 per person daily.

Among the major additions to local skiing:

* Wintergreen in Virginia's Blue Ridge Mountains unveils "The Highlands," three new expert slopes and a triple chair, part of a $2 million expansion program this year. The vertical drop is 1,003 feet and the longest run is 4,450 feet. The resort also has added a water-cooling device to its snow-making system, to drop water temperatures 8 to 15 degrees. The result is they can make more snow faster and earlier in the season.

* Jack Frost in Pennsylvania's Western Poconos is opening five new slopes and a wooded glade area on East Mountain for advanced skiers as part of a $6 million expansion. Snow Ridge, a new 320-unit slopeside village, will make overnight accommodations available for the first time at the resort ($745 a week for a two-bedroom home). With Big Boulder, a few minutes distant and under the same management, the complex provides 27 trails and 14 lifts.

* In addition to the condominium facilities, Snowshoe in West Virginia has installed two new triple-chair lifts servicing two more intermediate and one advanced trail down the lift line.

* Already famed in the mid-Atlantic for its downhill challenge, Elk Mountain in eastern Pennsylvania has added "Tuscarora," a 3,000-foot-long expert trail, as well as a new restaurant and cocktail lounge.

* Mount Timberline at Canaan Valley opens this year with a 2,000-foot T-bar servicing three beginner and intermediate trails 2,500 to 3,000 feet long. Next year's expansion plans call for a 3,600-foot triple chair and four more trails, with a 1,000-foot vertical.

* Blue Knob in western Pennsylvania has built 100 condos for on-the-mountain rentals. The wide beginners trail has been extended down to the accommodations, but the chairlift up won't be installed until next season.

* The top-of-the-lift trails at Camelback in the Poconos have always been fairly steep, so this season they cut a wide, wandering easy trail, "Julius Caesar," down from the mountain.

Practically all of the region's resorts have made some modifications to their facilities or programs (more snowmaking and night lighting, for example, at Laurel Mountain in western Pennsylvania) following a generally profitable season last year.

Bryce, a small family area in Virginia's Shenandoah Valley, continues to build a strong racing program, for older amateurs as well as young Olympic hopefuls. "Keep an eye on Bryce," advices Skiing Magazine executive editor Dinah B. Witchel in the November issue after witnessing the "Bryce Brats" in pursuit of trophies. Racing is another way resorts are holding on to the better skiers. Ski area manager Horst Locher has scheduled a racing camp, Dec. 20-24, for "classified" and recreational racers.

Pennsylvania's Ski Roundtop has adopted the Star Test program of the Professional Ski Instructors of America. Skiers must pass ability tests to earn bronze, silver and gold medals. They also are offering "video analysis." For $10, you can watch a tape of your downhill style and find out what you are doing right or wrong. Its sister slope, Ski Liberty, has purchased 2,000 new pairs of rental skis equipped with the Look/Nordica integrated binding and boot system.

In western Pennsylvania, Seven Springs is introducing its "Tiny Tots" ski school for youngsters from about ages 4 to 7: Ski lessons, snack, playroom activities, lunch, ski rental for $18 a day or $12 a half day.

With the limits of terrain and climate here, the Washington-area ski industry will never rival the allure of the western resorts such as Aspen, Taos and Park City. They've got the dramatic peaks, the deep powder and the golden glow of a warm alpine sun and more room to handle the crowds. And it's New England you head for to get the ultimate in steep thrills and trails that twist for miles.

But the ski areas of the mid-Atlantic, expanding to meets the needs of Washington's growing army of downhill enthusiasts, increasingly are becoming a vacation alternative, offering a fair approximation of the big-time resorts -- and that's still pretty good skiing.