Audio cassettes are no threat to guidebook publishers, but the sales of taped travel tours are being spurred by the current profusion of portable cassette players and recorders. And production of these cassettes continues to grow.

Taped tours of U.S. cities and parks and a few European countries have been available to travelers for years (often with the option of renting both player and cassette) -- along with foreign language lessons on tape and even dramatizations of books to help pass the time during long auto trips. But the expanding coverage of cities and other vacation areas is providing more variety in content and approach, for both walkers and drivers.

Larry Johnson, a manufacturer of taped auto tours since 1967, says sales of tapes are now exceeding rentals. President of Comprehensive Communications Inc., Johnson says that in addition to commercially produced tapes, travelers are using cassette players with blank tapes to add their own commentary and on-the-scene sounds from their destination. Then they can play their own travel tapes for friends at home or use the audio to supplement slide shows.

Two of the most recent tapes offered by mail, and in some bookstores, are excellent examples of basic differences in the concept of audio tours:

* "Grand Canyon," created by National Travel Tapes Inc. of Salt Lake City, Utah, weaves narrative, dramatization, music and sound effects into an informative production that also is entertaining. The 60-minute tape -- supplemented by a small, colorfully illustrated booklet on the canyon's history, geology, scenic points, accommodations, facilities and information sources with related book list and small map -- is designed to let you "hear what you're going to see."

Like other tapes in the series (cassettes on southern Utah and northern Utah are also now available), it is intended to help with pre-trip planning, to call attention to significant sights, to instruct and to serve as a souvenir.

NTT tapes are overviews, not point-to-point tours. And dramatic license may be taken occasionally: On one segment of the simulated Grand Canyon trip, for example, the listener goes along on the well-known mule ride down the narrow, precipice-rimmed Bright Angel Trail to the Colorado River and Phantom Ranch at the bottom of the canyon. The real-life adventure is not without some danger and requires full concentration from the riders, who are often nervous novices in the saddle and strung out in single file behind their alert wrangler-guide. There's actually little chance for extended conversation on the trail, yet on the tape the talkative guide breezily shares observations with members of his "group," who respond. Still, the comments are accurate.

NTT began introducing its tapes in the West last March, with distribution in shops at the Grand Canyon and hotels in Salt Lake City, but has just begun to market them in the East. Tapes currently in production are about San Francisco, Los Angeles, Yellowstone National Park, Grand Teton National Park, New Orleans and southwestern Colorado. Each tape with booklet costs $9.95, plus $1 for handling and shipping. The firm accepts Visa and Mastercard.

National Travel Tape Inc., 989 East 900 South, Salt Lake City, Utah 84105, (800) 641-1531.

* "Your Personal Guide to London," from Tours by Tape -- Nicholson, is an excellent example of the more standard, guided walking tour. The package consists of two 60-minute cassettes, with a pocket-size booklet of full-color street maps with index and information that includes places of interest, famous buildings and theaters. It is approved by the British Tourist Authority.

These tapes lead you almost step by step through specific itineraries. They cover Westminster, the Tower of London, the Heart of the City and Fleet Street, and BBC travel broadcaster John Carter's distinctly British diction helps set the proper mood.

Route directions, history, landmarks like Buckingham Palace and St. Paul's Cathedral and the city's culture and personalities are woven in with a bit of music and some sound effects. Tours by Tape Ltd., a British firm, entered the travel tape field four years ago in association with Nicholson, a popular London guidebook publisher. It opened a New York office only a few months ago to sell its tours in this country.

Tours by Tape is working on taped tours for Stratford Upon Avon, Warwick, Oxford and Edinburgh; translations are being made to broaden sales in other European countries, Spanish-speaking areas and Japan. The London set can be purchased by mail from the manufacturer for $16.95 postpaid.

Tours by Tape, c/o Reservation Systems Inc., 6 East 46th St., New York, N.Y. 10017, (212) 730-1486.

Admittedly, selecting the most suitable audio tour for your particular destination isn't easy. Unlike a travel guide, which you can skim through before buying to sample the flavor, style and breadth of information, you can't "read" a cassette until you buy it, open the outside wrapping and play it.

But the following list, of some other producers of travel tapes with a brief description of their products, may offer some guidance:

* Comprehensive Communications Inc., of Scarsdale, N.Y., has the widest selection of self-guided auto tapes of U.S. national parks and also offers tours of U.S. cities, Canada's Rockies, England and Ireland. Thirty-three tapes are available.

CCInc. designs its self-guided tapes to be both entertaining and factual, with music and sound effects. Each 90-minute tape on the park system has been checked for accuracy by authorities such as local historians and naturalists, according to Johnson. Cassettes are now available on the Great Smoky Mountains, Rocky Mountain, Grand Teton, Glacier and Yellowstone national parks; Canada's Banff and Jasper parks; Washington, D.C.; Gettysburg-Lancaster-Pennsylvania Dutch areas; Newport, R.I.; Mystic Seaport-New London-Stonington, Conn.; and 1,400 miles of touring in California (on 14 tapes).

The cassettes are sold by some bookstores, motels and chambers of commerce; the park tapes are available for sale or rent in park gift shops. Or order by mail for $10.95 each plus $1 postage and handling. A free catalogue is offered, and the firm retails the tapes of other manufacturers.

CCInc., P.O. Box 385, Scarsdale, N.Y. 10585, (914) 472-5133.

* Travelcassettes, of New Haven, Conn., was founded in 1982 by Annabelle Simon Cahn, an art historian who has produced tours of Paris, London, Rome, Florence, New York City and Washington, D.C. A Jerusalem cassette also is being prepared.

"I use the urban fabric -- what you see -- as a foil for a cultural discussion that emphasizes art and architecture but also includes history, social conditions, music and literature," she explains. The form is narrative.

Some bookstores stock the 90-minute tapes, but they are sold primarily by mail for $12.95-$14.95 each, plus $2 for postage and handling. Cahn also markets tapes of other companies and provides a free catalogue (a stamped, addressed envelope is requested).

Travelcassettes, P.O. Box 982, New Haven, Conn. 06504-0982, (203) 777-8242.

* Pathfinder Productions in New York offers five 90-minute tapes, each giving a guided walking tour of a section of the city -- Wall Street and Old New York; Midtown Fifth Avenue; Greenwich Village; Chinatown, Soho and Little Italy; and Millionaire's Mile (museum mile). The cassettes are sold by a few New York bookstores and by mail for $10.95 each, $1.50 shipping and handling (Mastercard and Visa accepted). Free brochure available.

1 Rockefeller Plaza, Room 1424, New York, N.Y. 10020, (212) 757-1460.

* Boston WalkAbouts/The November Co. Inc., of Boston, has one tape, "Boston's Freedom Trail," that blends narration, music, sound effects and dramatization to tell the story of the American Revolution during a guided walk along the downtown trail. The Freedom Trail passes historical points of interest and includes nearby monuments and shrines. The tape (about 60 minutes in the English version) is sold in Boston hotels, bookstores, by the tourist information booth at the start of the trail on Boston Common and by mail for $9.95 plus $1.50 postage and handling.

Boston WalkAbouts/The November Co. Inc., 50 Commonwealth Ave., Suite 702, Boston, Mass. 02166, (617) 262-1368.

While the market appears to be growing, not every tape product automatically meets with public acceptance. Travel Books Unlimited, 4931 Cordell Ave., Bethesda, Md. (951-8533), reports that Tours by Tape's London set is selling well, but the store recently had to return another firm's shipment of tapes on motor tours of France that weren't moving off the shelves.