THREE CHEERS for books on tape! They'll never replace the joy of reading, but they certainly do add fun and learning to otherwise wasted hours. I know: I've driven to Boston with Edith Wharton, raked leaves with James Bond, and jogged through Andromeda with Arthur Dent and Zaphod Beeblebrox. And I'm not alone. Americans are listening to all kinds of audio productions on their 300 million cassette players (of these, 45 million are personal stereos and automobile units).

Dozens of new cassettes offering a wide range of material are appearing every month. Most are abridged or (less commonly) full-length novels, but you'll also find short stories, plays, essays, lectures, interviews, and -- particularly in the self-help genre of stress reduction, weight loss, exercise, and business management -- original cassette productions designed for the listener on the move.

But unlike books that can be inspected in the store or public library, cassettes must be rented or purchased in order to judge the value of their contents -- highly variable, depending on the publisher and the work in question.

Most publishers of fiction cassettes, for example, use one performer (or the author) reading an abridged or adapted version of the book. Other publishers embellish their narratives with music and sound effects. Depending on the listener and the book, this electronic enhancement may be delightful or drecky.

Warner Audio Publishing, for instance, uses music and sound effects on their tapes, sometimes subtly and beneficially as on their production of two Robert Heinlein short stories, "The Green Hills of Earth" and "Space Jockey." But their version of Elmore Leonard's Glitz turns a good book into an over- produced cassette.

The story follows Miami cop Vincent Mora who's stalking and being stalked by Teddy Magyk, a crazy ex-con with a grudge, a sick sense of humor, and a semi-automatic pistol. Glitz races, as a Leonard saga always does, to an explosive climax.

So why did the cassette's producers glitz up Glitz by adding a background of syntho- pop music, crowd noise, traffic sounds, and gunshots? Leonard fans who enjoy letting their minds roll over the master's crisp dialogue and nuances will find this two-hour abridgement aural bubble gum.

Good novels don't need electronic sequins. Listen for Pleasure, one of the biggest audio publishers, offers many unenhanced readings -- one of their best being John le Carr,e reading The Spy Who Came in From the Cold.

A superb performer, Le Carr,e has a voice remarkably suited to his novel of espionage, deception and betrayal. He makes Alec Leamas sound burned out yet menacing; Control suitably smarmy, slightly effete; Mundt, the East German, flat and deadly. Le Carr,e raises his pitch subtly when reading a woman's part, adds an authentic twist of accent when reading the Germans, and sounds detached (almost wistfully sad) as narrator. Le Carr,e fans should enjoy this cassette as much as the book.

If your taste in espionage is a bit lighter, follow James Bond as he tries to unravel an international diamond smuggling operation in Ian Fleming's Diamonds Are Forever. Read by Ian Ogilvy, Bond sounds appropriately urbane whether routing thugs or romancing his current lady. Ogilvy doesn't do quite as well with the voices of the various Yank gangsters, however. His American accent goes awry and the hoods sound like the Bowery Boys of Budapest. But Bond's adventures are always good for a few laughs, so accept this as a bonus.

FOR MORE purposeful laughter listen to Leo McKern reading two stories from John Mortimer's The Trials of Rumpole. McKern, who plays the witty and cynical barrister on the Thames Television series, is pure delight on tape. A wonderful mimic, he gives each character an authentic voice, mannerisms, and accent, creating a consistently funny and intelligent audio tour of Rumpole's world.

Mortimer's cleverly subplotted stories -- "Rumpole and the Man of God" and "Rumpole and the Age for Retirement" -- will make many listeners instant Rumpole fans whether they've seen the television production or not.

Douglas Adams' The Hitchhiker's Guide to the Galaxy is another cassette just for laughs. Originally a 1978 BBC Radio series (heard here on National Public Radio), then a best-selling book and TV series, Adams' epic of space, time and convoluted whimsy is now a solo reading by Stephen Moore.

Moore (who played Marvin the Depressed Android in the BBC production) is in top form doing the voices of the numerous hyperspaced screwballs inhabiting Adams' cosmos. Some electronic special effects are used (echo chambers and bizarre voice filters) but they're artfully done, great fun to exrience on headphones, and entirely appropriate to the book.

The sequels -- The Restaurant at the End of the Universe and Life, the Universe and Everything -- are available from the same publisher, also read by Moore.

For more serious literature try Audio Book Contractors, one of the few cassette publishers producing unabridged works. This company restricts its titles to classics, offering, among others, Daisy Miller, by Henry James; Selected European Short Stories (Maupassant, Chekhov, Mann, and Munro) and Selected Short Stories by Edith Wharton. I was especially impressed with Flo Gibson's reading on the latter two. Her precise reading style is complemented by a deep and expressive voice.

Audio Book Contractors also offers the sturdiest packaging -- plastic book-shaped boxes that can be conveniently stored on a shelf. (Listen for Pleasure uses colorful cardboard book-like boxes with built-in cassette holders, while Warner Audio's tapes are housed in nearly impregnable blister packs that must be assaulted with a sharp knife and paid up Blue Cross.)

Bookcassettes also offers unabridged books -- but at outstanding prices -- $11.95 to $17.95. That's just what you'd pay for the hardcover book. There's a gimmick, of course, but a clever one: Bookcassettes can only be played on a stereo with balance control. First you play the left tracks on both sides, then the right tracks. By splitting the channels, Bookcassette's producers double the playing time, fitting a complete book on three to five cassettes. Personal stereos usually don't have balance controls, so Bookcassette offers an $8.99 adapter that lets you hear the story through both earphones.

Their titles include Heartburn, by Nora Ephron; The Brotherhood of the Rose, by David Morrell; Joseph Wambaugh's Lines and Shadows, and others. Some, like Wambaugh's, are read by individual narrators, but most Bookcassettes use several actors, dramatizing the book.

Unlike a play, however, dialogue in a novel uses attribution. I found it confusing to hear characters in these "performed" novels speaking their dialogue while being constantly interrupted by a narrator rapidly interjecting "he said," "he sneered," "she wondered." My bias is toward a lone, unenhanced skilled reader but many other listeners will enjoy the multi-voice approach.

Thus for maximum listening pleasure it's wise to read carefully the labels on cassettes (or their descriptions in the publisher's or renter's catalogue) before acquiring them. Be sure you're getting what you think you want -- abridged or uncut; embellished with music, sound effects, and a cast of actors; or one performer simply reading aloud -- before you pull out your checkbook and put on your headphones.