Millions of Americans go camping every year, which should be no surprise in a nation so rich in gorgeous landscapes. It's also one of the cheapest ways to vacation, especially for families. And this summer, the plunge in gasoline prices should make a camping trip an even better bargain.

Camping can be as simple as packing the family into the car and driving to one of the many state or federal parklands within three or four hours of Washington. A campsite is almost always cheaper than a hotel or motel; you can cook most or all of your meals to save on restaurant bills, and the cost of recreation (hiking, swimming, fishing) is usually minimal or nothing at all.

Even beginners should have little difficulty arranging a camping trip. Most of the equipment you will need, including tents and sleeping bags -- as well as trailers and motor homes -- can be rented, usually before you leave home. It helps, though, to possess a bit of pioneer spirit, which can make the idea of forsaking modern conveniences actually seem like fun.

Think camping, and the typical image that comes to mind is Mom, Dad and the youngsters gathered for a hearty breakfast around an open fire, the tall pines rising above their tent and a rushing stream or deep-blue lake just a few steps away. That's certainly a possibility, but it's only one of many camping options that range from rigorous backpacking treks into the high Sierras to sedentary getaways at a fancy motor-home resort by the sea.

It's important to know, early in the trip-planning stage, which best suits you and your family.

Vacationers looking for adventure can head into one of America's wilderness areas -- on foot, toting tent and supplies on their back; or by horseback, white-water raft or canoe. This is camping at its most basic, about as close to the country's frontier experience as you will find: no toilets, no hot showers and -- a day's hike from the nearest road -- no one but you and your companions to rely on if you get into trouble. It may sound daunting, but many tour outfitters offer wilderness trips for physically able beginners.

If you prefer more civilized comforts (a privy, as a minimum, or nothing less than an air-conditioned motor home), then you are a candidate for a drive-in campsite. There are an estimated 5,000 campgrounds on federal land -- including 105 National Park Service areas -- thousands more in state and county parks and about 10,000 more commercially operated campgrounds. They are located in the mountains, by the seashore, alongside the interstates, in big-city suburbs and even next to Disneyland and Disney World.

Some drive-in campsites can be almost as primitive and remote as those accessible only on foot -- though you might have to bounce over a long, rutted dirt road to get to them. Others by comparison -- and the splendid Fort Wilderness Campground Resort at Disney World in Orlando (beginning at $28 a night) is an example -- are in the heart of busy tourist land and seem almost luxurious.

Many campgrounds have hot-water showers, laundry facilities and swimming pools, and some even offer hookups for cable TV, if that's your idea of an outdoor getaway. You can sleep in a tent, a trailer, a van or try an apartment-sized motor home equipped with a full kitchen, bathroom and air conditioning. Motor-home rental agents say they can teach you to handle a large vehicle safely in an hour or two.

For some travelers, camping can be simply a way of getting some place else cheaply, an alternative to hotels and motels on the road to the grandparents' house. On the other hand, camping is often the whole purpose of the vacation, a chance to stay inexpensively for a week or two at a big resort area or a national park, enjoying the sea or mountain views and fresh country air.

An important reminder: For many camping destinations -- the most popular state and national parks and major resort areas -- reservations are recommended, and the sooner you can make them the better. Many popular campgrounds tend to be booked up weeks in advance during the busy summer months.

Among the many resources -- including advance-reservation phone numbers -- available when planning a camping trip:

*National parks: Some of the most spectacular scenery in the country is found in America's national parks. Depending on the park you pick, you can sun on a sandy beach (Cape Hatteras), climb winding trails to mountain glaciers (Mount Rainier), skinny-dip in a hidden pool (Yosemite) or explore ancient Indian cliff dwellings (Mesa Verde).

Most national park campsites are available on a first-come basis. In the summer, it can pay to show up early at the park to assure yourself of a good spot, particularly if you want to stay for several days. Stays may be limited to one or two weeks. The daily rate ranges from about $3 to $8.

At the 10 busiest parks, reservations (and advance payment) can be made at many Ticketron outlets for a $3.50 booking fee. Reservations are accepted up to eight weeks in advance of your planned arrival.

These parks are: Acadia National Park, Maine; Cape Hatteras National Seashore, North Carolina; Grand Canyon National Park, Arizona; Great Smoky Mountains National Park, Tennessee; Joshua Tree National Monument, California; Rocky Mountain National Park, Colorado; Sequoia National Park, California; Kings Canyon National Park, California; Shenandoah National Park, Virginia; and Yosemite National Park, California.

Reservations (and payment) can also be made at the Public Inquiry Office of the National Park Service, located just inside the C Street entrance of the Interior Department at 18th and C streets NW. It is open 9 a.m. to 5 p.m. Monday through Friday. You can call during these hours for the location of the nearest participating Ticketron office, 343-4747.

Mail-order reservation applications are available from the Ticketron Reservation Office, P.O. Box 2715, San Francisco, Calif. 94126.

The Public Inquiry Office also has informational brochures for each of the national park areas. A copy of "Camping in the National Park System, 1986/87," a guide to camping facilities in 105 parks, can be obtained by sending a check for $3.50 to Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Specify brochure number 024-005-009876.

Backpackers should consult the office of the superintendent at any park they are considering visiting to determine current back-country trail regulations and possible restrictions.

*Nearby state parks: An excellent variety of state parks offering campsites for weekend getaways or longer vacations can be found in the mid-Atlantic states of Virginia, Maryland, West Virginia, Delaware and Pennsylvania. They are located in the western mountains, along the Atlantic beaches, on the Chesapeake Bay and in the Shenandoah Valley. Facilities range from primitive (Sky Meadows in Virginia) to quite comfortable at Canaan Valley Resort State Park in West Virginia.

Each state's reservation policies differ, and fees vary according to the park -- though most are under $12 a night (a price for full motor-home hookups). For details on each state's park system, contact:

VIRGINIA: Virginia Division of Parks and Recreation, 1201 Washington Building, Capitol Square, Richmond, Va. 23219, (804) 786-2134.

MARYLAND: Maryland Forest, Park and Wildlife Service, Department of Natural Resources, Tawes State Office Building, Annapolis, Md. 21401, (301) 269-3771.

WEST VIRGINIA: Department of Commerce, Marketing Tourism Division, 1900 Washington St. East, Building 6, Room B564, Charleston, W.Va. 25305, (800) CALL-WVA or (304) 348-2286.

DELAWARE: Division of Parks and Recreation, P.O. Box 1401, Dover, Del. 19903, (302) 736-4702.

PENNSYLVANIA: Pennsylvania Bureau of Travel Development, 416 Forum Building, Harrisburg, Pa. 17120, (800) 237-4363 or (717) 787-5453.

*Commercial campgrounds: No camper who has driven any distance into the countryside can have failed to notice a KOA sign. The initials stand for Kampgrounds of America, which claims to be the largest commercial campground network in America. It has almost 700 campgrounds in the United States and Canada.

Initially, the network grew up alongside America's highways to provide inexpensive stopovers for travelers, according to marketing vice president Ken Zimmerman. In recent years, however, KOA has expanded into resort camping, with resort campgrounds, for example, at Myrtle Beach, S.C. (which titles itself the "Seaside Camping Capital"); the Florida Keys and adjacent to Disneyland at Anaheim, Calif.

Amenities vary by campground, but all of them are supposed to provide clean restrooms, hot showers and campsites for both tenters and motor-home vacationers. A majority have swimming pools, said Zimmerman, and a few provide cable-TV hookups. Rates vary, also, depending on the location. Through mid-September the charge at the Anaheim campground, among the higher-priced camping sites, is $23.95 daily for two people and $2 additional for each child.

For reservations, contact individual campgrounds. Directories to KOA's network are available free at any KOA site or can be ordered by sending $2 (for postage) to KOA, P.O. Box 30162, Billings, Mont. 59107.

The National Campground Owners Association provides a state-by-state list of its affiliates, which in turn are sources for listings of additional commercial campsites in each state. Send a stamped, self-addressed envelope to National Campground Owners Association, 804 D St. NE, Washington, D.C. 20002.

An excellent resource for other commercial campgrounds -- as well as national park, state and other publicly owned campgrounds (national forests, refuges and recreation areas) -- is Rand McNally's "Campground & Trailer Park Directory," an exhaustive guide to camping in the United States, Canada and Mexico. It sells for $12.95 in bookstores and camping supply shops.

At least one company, Leisuretime Reservation System Inc., is attempting to form a national campground rental reservation network. It currently represents about 200 commercial and public campgrounds in California; campgrounds in 21 Colorado state parks and a scattering of commercial campgrounds elsewhere in the West and on the East Coast. It can book a campground-to-campground driving trip, for example, on the Pacific Coast from Washington State through California. The reservation fee is $3.75 per campground on the itinerary, plus the daily campsite rental. For information about campgrounds represented: Leisuretime Reservation System Inc., P.O. Box 1010, Citrus Heights, Calif. 95611, (916) 722-5602.

*Motor-home (and other) rentals: You've picked a campsite, or a series of them, so now you need a shelter to sleep in and, perhaps, sleeping bags, air mattresses and a cooking stove. They can all be rented.

For shelter, the choices include a tent, a tent-trailer you tow behind the family car, a small live-in camping trailer (also towed) and a motor home. Motor homes come in a variety of lengths from 18 feet up to about 33 feet. Longer motor homes are more difficult -- and more expensive -- to drive.

Several nationwide firms rent motor homes and trailers, among them American Safari National R.V. Rental System of Miami Beach, Fla., (800) 327-9668; and U-Haul International, (800) 821-2712. You can rent a motor home in your hometown and drive to your destination or have one waiting near the airport if you are flying to a more distant part of the country.

American Safari operates 82 rental stations in 33 states. It offers motor homes in four sizes. Rates vary by the size of the motor home, the season, the location of the rental and whether you are returning the vehicle to the same place you picked it up.

For vacationers considering a trip to the Southwest to see the Grand Canyon, Monument Valley, and Bryce and Zion national parks, American Safari is quoting a price of $819 a week for a six-sleeper, 24-foot-long motor home picked up at Phoenix. The first 1,050 miles are free; additional miles are charged at 21 cents a mile. There is a charge of $25 per person for bed linens, tableware and other necessities. Insurance is also extra.

U-Haul, a famous name in truck and trailer rentals, has entered the recreational-vehicle rental business in a big way in the past two years. It offers motor homes and camping trailers at 450 outlets across the country, including several in the Washington area. It also rents a large line of other camping equipment, including tents and sleeping bags. (Equipment can also be rented at outdoor outfitters or borrowed from friends.)

If you are interested in a driving trip through the Colorado Rocky Mountains, U-Haul is offering a rate of $899 a week for a 27-foot motor home picked up in Denver. The price includes 1,000 free miles; additional miles are charged at 19 cents a mile. The cost for bed linens and tableware is $35, and insurance is extra. For a higher fee, U-Haul provides the option of picking up a motor home in one city and returning it in another.

U-Haul also rents a small sleep-in camping trailer. The rate from Denver is $175; car rental, to tow it, is extra, of course.

Listings for motor-home and camping-trailer rentals can be found in the Yellow Pages under "Recreational Vehicles." A national guide to recreation-vehicle rental agencies, "Who's Who in RV Rentals," can be ordered for $4 from the Recreation Vehicle Rental Association, Suite 500, 3251 Old Lee Highway, Fairfax, Va. 22030.

Informational literature about motor-home camping and an order form for recreation vehicle publications can be obtained by sending a stamped, self-addressed envelope (long size) to the Recreation Vehicle Industry Association, Dept. JY, P.O. Box 2999, Reston, Va. 22090.

Also available for rent to campers: A pop-up tent carried in a compact trailer towed behind your car. Tent-trailer rentals also are listed in the Yellow Pages under "Recreational Vehicles." The Pleasureland Travel Center of Alexandria charges $185 a week for a tent trailer, plus $1 a day for insurance and a 3 percent rental tax, (703) 780-0543.