(MONEY Magazine) – Unspoiled, unsung and largely undiscovered, America's 2,040 state parks are the nearest thing there is to having wilderness in your own backyard. Says Kathy Bartlett, Northeast regional director for the National Recreation and Park Association: ''State parks have tremendous variety, offering everything from oceans to mountains, especially in the East, where national parks are not as dramatic as they are west of the Mississippi.'' Besides being closer to home, state parks often offer more wide-open spaces. Last year, for example, the country's 50 national parks, including meccas like the Great Smoky Mountains and the Grand Canyon, attracted a record 57.4 million visitors. This year, the National Park Service expects 3.5% more tourists, the fourth straight year of such increases. ''The most popular of the national parks,'' complains Geoff Sundstrom at the American Automobile Association (AAA), ''are becoming overloaded.'' Our advice? Consider leaving national parks to the itinerant hordes and check into state wildernesses not far away. No one organization or agency speaks for all state parks. AAA guidebooks do include some details (books are free to AAA members; annual membership fees run from $18 to $65). But, state by state, information is scarce. To find the best dozen state parks in the U.S., we canvassed a select group of experts, notably: Ney Landrum, executive director of the National Association of State Park Directors; Barry Tindall, director of public policy at the National Recreation and Park Association; and Vici DeHaan, author of State Parks of the West (Cordillera Press, $13.95), a 13-state survey of 318 parks. DeHaan's guide to midwestern state parks will be published next year, and she has begun scouting in the East. Our picks were based on family- friendly facilities, the option of overnight camping, a choice of high- quality activities and the all-important ''ah!'' factor -- natural beauty and scenery. State-run parks range in size from two-acre W.B. Nelson near Newport, Ore. to one of the continental U.S.' oldest and largest state wildernesses, New York's 100-year-old, 6-million-acre Adirondack Park -- an area roughly as big as Vermont. The newest on our list? Eugene T. Mahoney, a 574-acre park designated in 1991, just outside Omaha. All 12 parks are open year round but many close some campgrounds during cold months or off-season. Vital statistics about each park are listed in the table on pages 154 and 155. Other tips: -- Most parks charge for admission or parking, even for day-trippers. Other fees, such as overnight camping charges, vary according to the site you choose within the park and who manages it. Some attractions, such as boat rentals, scuba diving or riding stables, may be privately operated. -- It's smart to make reservations (when possible); confirm prices and double- check facilities before visiting. Park rules change frequently, and local government cutbacks have caused some parks to trim services. For instance: Rest rooms at one California park are now cleaned twice rather than four times a day, two out of four permanent ranger jobs at an Alaska park remain unfilled since 1990, and a Wisconsin park can't afford the fishing pier planned to accommodate handicapped visitors. As a result of budget cuts, many state parks are now raising admission prices or charging user fees. -- If the park does not accept reservations, assume campsites will fill early during high-season weekends, so you should arrive by 8 p.m. Friday evening. Occasionally, daytime parking may also be limited: On summer weekends, for example, the 1,000 parking spaces at Wisconsin's Devil's Lake are usually filled by noon. -- Call ahead to check logistics and amenities. Some parks have no nearby grocery stores or shops. In Denali State Park in Alaska, for instance, the nearest place to stock up on groceries is 100 miles south. -- If you're interested in naturalist or guided activities, plan trips during prime season. Ranger programs and children's activities (usually free or $1 to $5 daily) are normally held from May through October. -- Generally, pets are allowed, but you'll have to keep your animals on a leash in certain areas.

BOX: SUMMER '92

One out of every five travelers will choose an outdoor vacation.

82% of vacationers will travel by auto, truck or RV.

Road trips: Southeast, 29%; Northeast, 13%; Midwest, 35%; West, 19%; Mexico/ Canada, 4%

CHART: NOT AVAILABLE CREDIT: NO CREDIT CAPTION: WHAT TO KNOW BEFORE YOU GO Even wilderness has its limits. Some pointers: -- Planning. Parks often maintain several phone lines. We list a main in formation number and, when possible, another for reservations. -- Fishing. Most parks require fishing li censes. Expect to pay a $10 to $40 fee, de pending on the state, the park, your resident status and when the permit expires. -- Boat rentals. Rates vary. Typically, hourly fees start at $2.50 for canoes and go up to $30 for powerboats. Fuel or oil may be extra.

-- Campsites. Sites run the gamut of comforts and many are quite primitive; don't make assumptions. You'll usually share commu nal water supplies when there aren't any individ ual water hookups. -- Groups or reunions. Some parks limit the number of people at each campsite. Check in advance.