August looms. That means it's decision time for even the most practiced of summer-vacation procrastinators. If an outdoor getaway appeals to you, several recent guidebooks can help you choose from among some unusual possibilities. Will it be tracking America's rich Indian culture -- or fishing the streams of a national park? Should you opt for a guest ranch -- or a houseboat on a quiet lake? Explore the natural splendors of the Caribbean -- or hike the Appalachian Trail?

Most of these new guides have negligible literary value; they are meant to be used as reference books. Some are no more than compilations of information unavailable in any other single source; "Lodgings Along the Appalachian Trail," for example, is a new series published by the Appalachian Trail Conference for hikers who don't want to spend every night of their journey in a tent. Others, such as "Hidden Florida Keys and Everglades" by Candace Leslie, provide at least some critical evaluation based on the author's personal observation.

The prettiest of the selection is Kay Showker's "Caribbean: The Outdoor Traveler's Guide," filled with full-page color photos of rain forests, deserts, mountain peaks and other examples of the region's natural beauty. The most welcome, perhaps, is "Indian America" by Gary McLain, who uses his Choctaw name -- Eagle/Walking Turtle -- on the cover. It highlights 300 Indian tribes, detailing which ones welcome visitors with ceremonies, arts, crafts and historical sites.

Among the useful new outdoor reference guides:

"The National Parks Fishing Guide" by Robert Gartner (Globe Pequot, 445 pages, $14.95): Vacationers headed for scenic Yellowstone National Park in Wyoming may expect to find good fishing, and they will, according to the author. The surprise is that many of the nation's historical parks can be fished also, among them Valley Forge National Historical Park outside Philadelphia. The Schuylkill River in the Valley Forge, he writes, "is one of the best bass streams in Pennsylvania."

Aimed not just for the fishing enthusiast, the book should be of use also to travelers whose primary interest may be the scenic or historical attraction of a national parkland but who also want to take a break from sightseeing to do a little fishing. It details fishing possibilities in 125 of the country's national parklands, large and small. There are five in Maryland, nine in Virginia and three in West Virginia.

Among the possibilities are surf casting for bluefish on Cape Cod National Seashore in Massachusetts, charter boat fishing for swordfish and striped marlin off Channel Islands National Park in California and remote wilderness fishing in Isle Royale National Park in Michigan.

Tips on how to fish are included, but the emphasis is on where to fish, and the book gets quite specific. It names a number of lakes in the Rocky Mountain high country where fishing is good but cautions that many other high mountain lakes are barren of fish. For fishing outings close at hand, it lists access points for 42 trout streams in Shenandoah National Park in Virginia. Consult this guide when you are headed for a national parkland. It may convince you to take along some fishing gear.

"Ranch Vacations" by Eugene Kilgore (John Muir, 344 pages, $18.95): The Old West is still alive, and probably the best way to enjoy it is at a guest ranch where those cowboy boots you bought in the city really have a purpose. Horseback riding is the primary recreation, but many ranches offer swimming pools, tennis courts, hiking trails and trout streams and lakes. Riding experience is not necessary; it only takes a few minutes to learn enough to manage a horse on trail rides. But many ranches will teach you more advanced skills so you can participate in the guest rodeo at the end of the vacation.

Kilgore, a former cowboy himself, describes more than 200 guest ranches, all but a few of them in the Rocky Mountain West. Most welcome families. They range in style from very rustic places serving traditional home-cooked meals to elegant ranch lodges with a gourmet chef in the kitchen. Each ranch gets a separate page in the guide, and there are photographs of many of the ranches. I have stayed at two of those included, and I found Kilgore's treatment of them adequately detailed and accurate.

He is as impressed as I was with the magnificent waterfall that plunges down a mountainside for 1,000 feet in full view of the cabins at Beartooth Ranch near Nye, Mont. And he cites the inviting handmade rocking chairs that line the porch of the lodge at Idaho Rocky Mountain Ranch in Stanley, Idaho. Most guests settle into them to watch the sun set behind the spectacular Sawtooth Mountains.

Kilgore distinguishes among several kinds of guest ranches, which is a big help in planning a ranch vacation. They include small, family-run guest ranches; fancier resort ranches, where riding competes with many other activities; working cattle ranches that offer you a chance to play cowboy; fly-fishing ranches; hunting ranches; and cross-country skiing ranches for winter vacations.

As a useful addition, he has listed major American museums with collections of Western art or artifacts, such as the fascinating Plains Indian Museum in Cody, Wyo. Also included are the country's top 20 annual rodeos; wagon train operators offering covered wagon vacations; and major Western events, such as Cheyenne's annual Frontier Days celebration (which runs this year through July 29).

"Floating Vacations" by Michael White (John Muir, 248 pages, $17.95): No, this is not another book about Caribbean cruises. Author Michael White's floating vacations are more adventurous. He has compiled an extensive listing of outfitters -- 700 companies in all -- offering houseboat rentals, canoe and white-water rafting excursions and fully crewed yacht charters in North America and the Caribbean.

The trips range from primitive to luxurious, but they all have one thing in common, says White, who captained a charter yacht in the Virgin Islands for five years. None of them requires any previous boating experience. More than a listing, however, the book provides considerable detail on how to organize a trip and choose a safe outfitter. The material covered should be of considerable assistance to a first-timer considering any of these floating trips.

The informative section on houseboats provides an illustrated chapter on maneuvering these floating apartments. The white-water rafting section makes important distinctions among types of rafts -- some you paddle, others are handled by a guide, and the larger ones have motors. In the yacht charter section, advice is offered on how to pick the yacht that best meets your needs and interests. Cabin size, whether berths are single or double and the speed of the yacht are all important aspects of a decision.

"Caribbean: The Outdoor Traveler's Guide" by Kay Showker (Stuart, Tabori & Chang, 495 pages, $19.95): The Caribbean has much more to offer a visitor than pretty beaches and sunbathing, as this attractive new guide illustrates. It is an incentive for deserting tourist enclaves to explore the natural beauty found beyond the beaches.

But fine scenery is not the book's only appeal. It also serves as a handy resource guide for rigorous outdoor activities not normally associated with a Caribbean beach vacation, such as hiking, mountain climbing, caving, horseback riding, river rafting, white-water canoeing, birding and deep-sea fishing.

The book is organized on an island-by-island basis, with descriptions of community and national parklands, gardens, waterfalls, streams, lakes, hot springs, swamps, mountain valleys and other natural attractions -- many of them overlooked by most tourists. The text is complemented by excellent color photographs by Gerry Ellis. The guide should appeal to more adventurous travelers.

"Lodgings Along the Appalachian Trail," a series published by the Appalachian Trail Conference: These three booklets are listings, nothing more, but they are very useful nevertheless. The guides are designed for hikers who wish to spend a weekend or more on the Trail without backpacking.

The length of the trail from Georgia to Maine is covered in the booklets, one each for Southern states, mid-Atlantic states and New England. Within each geographical area, the trail is further subdivided. Shenandoah National Park, for example, is one of six chapters in the mid-Atlantic states guide. For each subdivision, there is a comprehensive listing of nearby lodgings, including hotels, motels, bed-and-breakfast inns, youth hostels, cabins and campgrounds.

The listing for each lodging includes in chart form such helpful planning information as address, phone number, distance from the trail, room rates, dining facilities, office hours, what credit cards are accepted, overnight parking possibilities and transportation (if any) to the trail.

The Southern and New England guides are $5.95 each; the mid-Atlantic guide is $4.95. They are sold in camping supply and outdoors stores. They also can be ordered from the Appalachian Trail Conference, P.O. Box 807, Dept. SD, Harpers Ferry, W. Va. 25425. Enclose an additional $2.20 for shipping.

"Indian America" by Eagle/Walking Turtle (John Muir, 413 pages, $16.95): This is an exceptionally handy resource for travelers interested in Native American cultures. It describes more than 300 tribes, providing information on where to find them and when public ceremonies, if any, are offered. Some tribal areas welcome visitors; many do not.

In the section on the Great Plains, for example, Eagle/Walking Turtle cites the Crow Fair of the Crow Tribal Council in Hardin, Mont., as "one of the biggest powwows in the lower 48 states" and "one of the best." Held annually in August (Aug. 1-6 this year), it is a picturesque congregation of colorful tepee lodges. A major feature is an all-Indian rodeo, and there are powwow dances, a parade, exceptional beadwork and other crafts and Indian foods. Nearby is the Custer Battlefield National Monument.

In addition, the book includes such helpful lists as all-Indian arts and crafts shows held annually; Navajo rug auctions; Indian museums with major collections on American Indians; Indian-owned or Indian-operated museums and cultural centers; Indian rodeos and Indian-owned stores. Throughout the book, advice is offered on the proper etiquette in visiting Indian sites, many of which are considered sacred.

"Hidden Florida Keys and Everglades" by Candace Leslie (Ulysses, 142 pages, $6.95): You might want to skip Everglades National Park in the summer because of mosquitoes, warns author Candace Leslie. But in the Florida Keys, sea breezes keep mosquitoes down and daytime temperatures pleasant. The added attraction is that summer lodging prices in the Keys are much lower than during the winter high season.

Fishing, boating, snorkeling and scuba diving are the primary activities in this string of tropical islands, and Leslie directs readers to the places where these sports can be pursued. She also favors offbeat attractions, scenic hikes, quiet lodgings and small restaurants away from the busy Overseas Highway that links the Keys in a series of 42 bridges. Her critical evaluations are very helpful.

Without Leslie's book, you might drive the 113-mile Overseas Highway from Key Largo to popular Key West without stopping. With it, you almost certainly will slow down for a better look.