SO WHAT'S all the fuss about no-frills airlines? You'd think traveling cheap was a new idea. On the ground, the concept's been thriving for half a century in the form of youth hostels, which offer clean, simple and safe overnight accommodations at a nominal fee in scenic, cultural and historic locations.

"We are here to encourage outdoor recreation," says Lynn Powers of the American Youth Hostels headquarters here.

Members can stay overnight for as little as $3 to $11 -- a traveler's dream and Hilton's nightmare -- at a national network of nearly 300 hostels ranging from a remodeled lighthouse on the California coast to an authentic Canadian Pacific Pullman railroad car or a Colorado dude ranch, a 182-year-old Philadelphia mansion set in the woods of one of the world's largest city parks, an 1873 lifesaving station oNantucket Island and renovated hotels, school dormitories, former military facilities and even private homes.

Locally, there are more than 20 hostels within a four-hour drive of Washington -- at Leesburg, Urbanna and Buchanan in Virginia, for example; Knoxville, Betterton and Cambridge in Maryland; plus a string of Pennsylvania locations. Many are ideally situated for hikers and cyclists out among the fall leaves. Although nearly all hostels welcome automobiles, most are designed for folks traveling under their own steam.

Most hostels vary greatly in the way of creature comforts, yet each has a certain charm. For example, Pennsylvania travelers will find the nation's oldest continously operated hostel along state Route 625 in Bowmansville. Built in 1820, this stone and wooden-frame building has been operated as a hostel since the mid-1930s, when it shared quarters with the small town's general store.

In olden days, Bowmansville was the second in a five-part hostel chain that streted nearly 65 miles throughout the Pennsylvania Dutch country of Lancaster County. Every ten to 20 miles along the pike, hikers and horsemen could find shelter and friendship without dipping deep into their pockets. Today, Bowmansville is one of only two hostels left in the chain.

First-timers may be surprised at Bowmansville's spartan conditions -- modernization stopped 23 years ago when bathrooms with hot and cold running water were introduced. Yet that starkness somehow provides a great deal of charm in the heartland of Mennonite and Amish farmers. (The $5 charge doesn't hurt, either.)

One large room provides space for preparing meals, a communal dinner table and an area for sitting and chatting with fellow travelers.

The guest's horses, once kept in the stables behind the house, have been replaced by ten-speed bicycles.

Carl Hess, a junior high school teacher who, with his wife Nancy, has operated the hostel for the past three years will also arrange a country dinner at the home of a local farmer who usually charges only a few dollars for a near feast. All it takes is a little advance notice.

Less than 60 miles to the east is Philadelphia's Chamounix Mansion. Built in 1802, the restored mansion overlooks the City of Brotherly Love in a beautiful 8,900-acre park. The first city-owned hostel in the U.S., it sleeps up to 60 visitors in the summer and 40 in winter. Inside, fine crystal chandeliers and brass lanterns light huge common rooms where guests can watch television, read and share experiences. Coin-operated washers and dryers are available in the basement along with a game room, a kitchen and dining room. In the surrounding park are tennis courts, a summer theater, an exposition hall, several art museums, a zoo, playgrounds, historic homes and tree-lined hiking trails. All this for $5.25 per night.

"American hostels are not as strict as those in Great Britain," said David Matthews, a 22-year-old Englishman from Buckinghamshire, as he sat in the Chamounix Mansion living room recently. "There, you have to get up a lot earlier and you have a lot more chores. There is more social responsibility." Matthews was enjoying a lengthy chat about his American travels with a fellow Brit, Kathleen Boardman, 21, of West Yorkshire. The pair, who had first met earlier that evening at dinner, later discovered that they had once lived within two blocks of each other in England.

On Maryland's Eastern Shore, Albert and Annette Atkinson run a hostel in part of their giant Victorian home in Cambridge. Although the home can handle ten visitors, "I prefer no more than six to eight at any one time," says Annette. She once had 13 cyclists from New York City and "some of them had to sleep on the floor." The Atkinsons, who have averaged 75 overnight guests annually since they joined the network in 1981, charge $5.25 per night.

Home hostels are "more like a bed-and-breakfast inn without the breakfast," says Doug Maas, national diretor of hostel operations. And the Cambridge hostel, with its wonderful atmosphere -- family pets included -- is a perfect example.

Within a mile, sailing fans can find their recreation on the Chesapeake Bay, while bird lovers are within ten miles of the famous Blackwater National Wildlife Refuge. In this region, the changing of fall's leaves is hardly a match for the annual migration of the Canada geese that stop by the hundreds of thousands along the banks of the Blackwater River.

The novice should be warned in advance that hosteling isn't for everybody. It's strictly a "do-it-yourself" proposition. Hostels provide a place to eat, sleep and wash. There is no one to carry bags, make your bed, fix your breakfast or pick up after you. In addition to insisting that the premises be left in the condition they were found, most hostel managers ask guests to perform some minor chores, such as sweeping the floor or taking out the trash before departig.

Bathing facilities are separate for men and women. Sleeping areas are also separated by sexes in dormitory rooms with six to ten beds and sometimes more. Guests are expected to provide their own sleeping bag or sleeping linens (some operations rent sheets), and to bring their own soap, towel and washcloth. While cookware generally comes with the communal kitchen, eating utensils are less likely to be provided. In any event, the finicky table setter will be hard-pressed to find matching silverware, and travelers are smart to bring their own knife, fork and spoon.

Large common areas give road-weary travelers a chance to relax, trade tips and tell stories. And Americans can enjoy the international flair of hosteling, as many guests come from Australia, Germany, France, England and many other countries.

Most hostels close during the day and reopen in late afternoon. Curfews -- usually earlier in the country hostels and later in the city -- are imposed, and travelers are asked to check out before midmorning. Drugs, alcohol and pets are prohibited, while smoking is restricted to approved areas. Stays are usually restricted to three nights in a row, and not all hostels are opened year-round.

Despite these restrictions, a growing number of travelers are discovering hosteling. Last year, 287,000 overnight guests -- 106,000 of them American -- stayed in U.S. hostels.

There are no age restrictions. The word "youth" simply implies a state of mind rather than age. The inexpensive overnight rates apply to card-carrying members whose annual dues are $10 for 17 and under, and 60 and over; and $20 for members 18 to 59 years old. Cheaper three-year and life membership plans are also available. One-night introductory membership passes may be purchased for $3 over the cost of a night's stay at any hostel. As a special golden anniversary offer, nonprofit groups that apply before September 30, 1985, will be given a free two-year membership. HOSTEL HOSPITALITY

If you're interested in hosteling, you can write: American Youth Hostels, National Administrative Offices, 1332 I Street NW, Suite 800, Washington DC 20005, or call 202/783-6161. Members receive a handbook that lists and rates all the hostels. It's available to nonmembers for $5.