We've just returned from a six-week, 9,500-mile cross-country driving trip. We threw two girls (ages 10 and 11), four sleeping bags, too many suitcases, and a "research" bag of guide books in the back of our station wagon and lit out for the territory.

In Colorado, we bought ice-cream cones for 20 cents a dip. When we asked a Utah storekeeper for a freezer bag, he replied, "That must be one of them uptown things; this is country." In Wyoming we saw both ends of a rainbow; there was not a pot of gold at either of them. A sign in a yard in Cody urged, "Get us out of the United Nations!" In Yellowstone, a 9-year-old Texan kissed one of our girls at a square dance.

Twice we camped under the stars: once in a desert and once near the Grand Canyon. More than half the time we stayed with friends and relatives. Between times, we sought out cheap, quiet motels. Half the time we picnicked. When we ate out, we tried to eat "local" -- Mexican food in Los Angeles, clam chowder along the coast, rhubarb custard pie in Iowa.

Food and lodgings became the practical focus of our days, and we soon discovered that many of the guidebooks we'd tossed in our research bag were worthless. Those we found useful are listed below. Maps

Although we carried several maps, including an American Automobile Association Triptik, time and again we returned to our Rand McNally Road Atlas ($5.95), an oversized book of color maps that gives you the big picture on mountains, rivers, interstates, big and little towns, mileage between points. (By the end of our trip, both girls knew how to read maps.)

For our hikes in the national parks, we were happy to have the U.S. Geological Survey maps picked up from the USGS mapstore in the GSA building on F Street between 17th and 18th Streets (343-8073). Maps with that amount of detail aren't available in the parks, although many other useful publications are.

(Along the way, we found that maps made by H. M. Gousha, available in many drugstores and some gas stations, are full of inaccuracies.) Where-To-Eat Guides

Someone, somewhere, should do a decent book on where to eat in out-of-the-way America--particularly where to eat near interstates. Most travel guides deal only with big cities, but with a car full of suitcases and cameras and sleeping bags we were reluctant to stop for meals in urban areas -- and weren't often near them, anyway. The food recommendations in the Mobil Travel Guides were bland, bland, bland. Other sources, besides blind luck and tips from locals:

Best Restaurants . . . a series published by 101 Productions, $3.95 each. Reliable guides to food in New York, Philadelphia, Florida's Gold Coast, Los Angeles, San Francisco, New England and the District.

Roadfood by Jane and Michael Stern, Random House, $7.95. Hungrymaking prose by homemade pie addicts, but in 9,500 miles of travel we came near only three of the places mentioned; one was closed, and one was mediocre.

Where to Eat in America, ed. William Rice and Burton Wolf, Random House, $7.95. A reliable guide to food in 50 cities, but not the food bible for people on a budget or an interstate. Where-To-Stay Guides

Mobil Travel Guides ($6.95 each). Head and shoulders above their competitors. Charm is not something they pay attention to, but otherwise listings are more extensive and detailed than everyone else's -- and they list accommodations in towns other guidebooks don't even mention. When it's 7:30 p.m., you're too sleepy to drive any more, and the next town is 65 miles away, this is the kind of book you're glad you brought along.

AAA Tour Books. Though less ambitious, also pretty good about listing lodgings in small-town America. If you plan to stop at the budget motels that have sprung up all over the country, be sure to make a confirmed reservation ahead of time as they fill up early in the day; most guidebooks list 800 numbers for budget chains.

Of the other main guidebook series, Frommer's Where to Stay USA, $3 to $25 a Night is better than Fodor's Budget Travel in America 1982. (Fodor has few listings and no addresses or phone numbers.) The Frommer and Fodor regional guides are much better than their national guides.

United States 1982, ed. Stephen Birnbaum (Houghton Mifflin, $10.95) is a once-over lightly guide, mainly to cities.

If you plan ahead, if where you stay is an ultimate destination and not just a place to sleep, if you want something with charm, or rock-bottom prices, these guides may be of interest:

America's Wonderful Little Hotels and Inns, ed. Barbara Crossette, Congdon & Weed, $12.95. Over 500 places, described by friends and readers of earlier editions.

Bed and Breakfast U.S.A. by Betty Rundback & Nancy Ackerman, Dutton, $5.95. Brief descriptions of 300 private homes available as tourist homes and guest houses, plus 40 reservation services for B&Bs in different parts of the country.

Bed & Breakfast, American Style, by Norman T. Simpson, Berkshire Traveller, $7.95. Like the author's Country Inns and Back Roads ($7.95), this truly focuses on 270 charming-sounding inns, mainly in the Northeast.

Country Inns of the Far West, by Jacqueline Killen and Charles C. Miller, 101 Productions, $6.95. 136 West Coast Inns, Mexico to Canada.

Farm, Ranch & Country Vacations by Pat Dickerman, $7.95, describes working and dude ranches and farms where cityfolk can milk a cow or ride a horse. (The author's Adventure Travel, $7.95, tells you where to ride a raft, join a cattle drive, rent a houseboat, or ascend in a balloon.) Available from Adventure Guides, 36 E. 57th St., N.Y., N.Y. 10022. Add $1.50 for shipping.

Hosteling U.S.A. by Michael Frome, East Woods Press, $6.95. The official guide to American youth hostels, no-frills lodgings (average $4 a night) geared to non-motorized travel: hikers, bikers, and the like.

Let's Go, U.S.A. by Harvard Student Agencies, St. Martin's Press, $6.95. A savvy guide to low-budget travel, city-oriented but better-than-average on lodgings and eateries.

U.S. and World Wide Travel Accommodations Guide, $5.95 from Teachers Tax and Travel Service, 1303 E. Balboa Blvd., Newport Beach, Calif. 92661. Information on 330 universities here and in Europe that offer lodgings, and sometimes meals, at ultra-low rates.

Very Special Places by Ian Keown, Collier, $9.95. A guide to 200 romantic inns, hotels and resorts, for lovers with deep pockets. Camping & Park Guides

A few weeks before our trip, a National Park Service expert was asked to rate the books on camping and parks most reliable and useful to him. His list and comments:

The Complete Guide to America's National Parks, by the National Park Foundation (a government-chartered, private foundation), $7.95. A decent, though not exhaustive, compact guide on how to get to, and where to stay in, over 300 areas of the national park system.

National Park Guide by Michael Frome (Rand McNally, $7.95) and Rand McNally Campground & Trailer Park Guide, Eastern and Western Editions, $6.95 and $5.95.

"For what they try to do, the Rand McNally books are probably the best there are, and the most accurate," says the National Park Service expert. "Unfortunately, they omit many useful locations like Assateague Island National Seashore."

Frome's book is a succinct, well-written, informative description -- with maps and photos -- of what you'll find in the 48 officially designated national parks. The Campground and Trailer Guide contains detailed charts of information.

National Parkways Series, a real value in guides to six national parks: Yellowstone, Grand Teton, Rocky Mountain-Mesa Verde, Bryce Canyon-Zion, Glacier-Waterton and Grand Canyon. Handsome oversize paperbacks with stunning color photographs, comprehensive texts. Prices under $5, plus postage, from World-Wide Research & Publishing Co., P.O. Box 3073, Casper, Wy. 82602.

The Random House Guide to Natural Areas of the Eastern United States by John Perry and Jane Greverus Perry, $11.95. "Overall, an outstanding work. The authors are to be commended for finding so many public facilities. Few sources even know of the existence of the Nature Conservancy's Virginia Coast Reserve."

We hope they'll do the rest of the country, too. Miscellaneous Guides

The Discount Guide for Travelers Over 55 by Caroline & Walter Weintz, Dutton, $5.75. Information on senior-citizen discounts for transportation, lodgings, food, even ski lifts.

The Great American Countryside by Val Landi, Collier Books, $24.95 cloth, $12.95 paper. An absorbing field guide to the animals, plants, geology, weather systems and other natural (and some man-made) phenomena of America.

A Guide to Music Festivals in America by Carol Price Rabin, Berkshire Traveller, $6.95. Classical, opera, jazz, folk, bluegrass, country, old-time fiddlers, tra la.

Guide to the National Wildlife Refuges by Laura and William Riley, Doubleday Anchor, $11.95. Tells how to get to America's 365 national wildlife refuges and what you'll find there.

The Literary Guide to the United States, ed. Stewart Benedict, Facts on File, $15.95. From Thoreau to Kesey, a book buff's travel companion.

Train Trips by William G. Scheller, East Woods Press, $7.95. Tips on present-day train routes and the cities the trains stop in.

Vagabonding in the U.S.A. by Ed Buryn, And/Or Press, $9.95. An offbeat guide in the Whole Earth Catalog tradition, packed with information, including a wonderful Resource Guide on travel books.