BUYING A BOOK is a relatively easy task, particularly if it's a classic. The reader knows, for example, that Stephen Crane's The Red Badge of Courage will contain essentially the same text in every unabridged edition no matter who publishes it in whatever type face, with or without illustrations. But purchasing a recorded book raises several important questions:

*Has the book been abridged? Once only Reader's Digest made an industry of condensing books, cooking novels down into literary residues which, like dehydrated pea soup, were recognizable by the lumps and could be reasonably palatable if nothing more nourishing was available.

Now producers of recorded books and their Procrustean elves are condensing again, trimming and paring away the flesh of even the most sacrosanct classics. You can buy, if you wish, a recording of Moby Dick (read by actor George Kennedy) that fits neatly on two cassettes. Running only three hours, it's perfect for the Type A listener. ("Just give me the bottom line, Ishmael.")

*Is abridgment an evil practice that devalues literature or is it a cost-cutting device that makes recorded books more widely available and less expensive? (A full-length recorded book costs at least twice as much as an abbreviation.) The answers are yes and no -- in either order, depending on your tastes and budget. Yet abridged is, after all, a euphemism for shortened -- probably not what the author had in mind when he or she produced the original work.

*Who is the reader and how does his or her voice and interpretation affect the material? Having the author read her own work is a fine idea if the writer is also a good reader -- or better, an accomplished actress. The choice of reader is crucial because recorded books aren't really books at all but, at their best, one-to-one performances experienced intimately through the earphones of a personal cassette player or car stereo speakers. Recorded books at their worst are uninspired readings from an electronic podium.

BOTH QUESTIONS -- that of abridgment and choice of reader -- are happily resolved in at least one example, the recent release of Big Blonde and Other Stories (Newman Communications), by Dorothy Parker, read by Lauren Bacall. The two hours of stories are presented uncut, which suggests that cassettes and short stories were meant for each other. And Bacall, the perfect reader for Parker's work, is wonderful.

Her deep, burnished voice and clear enunciation are at their best on the title story, "Big Blonde," the tale of a woman awash in gin and ennui. Bacall's performance makes the sadness palpable. The second story -- "You Were Perfectly Fine" -- is also about the darker side of boozing, but here Bacall's interpretation captures Parker's sly humor. Other stories in the set include "Cousin Larry," "Horsie," and "Lady With a Lamp."

Richard Crenna is another actor ideally suited to recorded books thanks to his early career as a radio performer (he played, among other roles, Walter Denton on Our Miss Brooks). Crenna is particularly effective on Listen for Pleasure's abridged version of The Red Badge of Courage.

Approaching the microphone intimately, playing his voice as he might an instrument, Crenna expertly uses dramatic pauses to heighten tension. He's especially good at dramatizing the soldiers' accents, making each man -- and especially Henry Fleming, the young protagonist -- fully developed characters.

The soldiers' voices present a special problem for performers -- and ultimately for listeners -- because while Crane wrote them in dialect, he didn't specify their regional origin. When Frank Muller reads the men's parts on Recorded Books' unabridged version (over twice the length of Crenna's reading, which gives you an idea of what abridgement, however well done, does to a novel), the soldiers and Henry's mother speak with a decided twang, sounding vaguely Southern. The aural effect was unsettling to me since Crane was writing primarily about Northern troops who, I presume, would have sounded differently.

Jack Dahlby, who narrates G.K. Hall's unabridged version of Crane's story, has a classic radio announcer's deep and resonant voice. His phrasing is more clipped than Muller's slowly paced delivery, but Dahlby so underplays the soldier's accents that the rural vernacular almost vanishes in the process.

Choosing between these three versions of the same story isn't easy. Crenna's is the best performance, yet it's abridged. But Muller's and Dahlby's full-length readings are certainly excellent and worth the price of purchase, my criticism being a relatively minor one. And, to further complicate your choice, Dahlby's six-cassette set also includes a bonus -- his readings of Crane's "The Bride Comes to Yellow Sky," "The Open Boat," and "A Mystery of Heroism."

Another classic done in two versions presents similar problems for cassette buyers. Nathaniel Hawthorne's The Scarlet Letter has been done by four-time Emmy winner Michael Learned (best known for playing Olivia on The Waltons) and by Washington's Flo Gibson, consistently one of the best cassette readers at work.

Learned's voice is light and warm, her diction and phrasing precise. Gibson's voice is deep and sonorous and ideally suited to characterizations of either men or women. Both performers are equally adept at breathing life into Hawthorne's anguished characters. The major difference between the two versions is that Learned's is abridged and Gibson's is full-length. Both readings are excellent.

Does having the author read his own work on cassette enhance the performance? Sometimes. The late David Niven's reading of his autobiographical The Moon's a Balloon and its sequel, Bring on the Empty Horses (both from Newman Communications), is delightful entertainment. The books were successful because they made good reading, but hearing Niven's adventures as a British soldier, bootlegger, actor and war hero recounted in his own witty and urbane style makes these tapes doubly pleasing. No other reader could have brought as much to the cassettes.

YET HAVING the author narrate his or her personal experiences is quite different from having writers read their fiction. Ray Bradbury reading his classic The Martian Chronicles is a case in point. Both the abridged (Newman) and full-length (G.K. Hall) cassettes open with the same informal monologue (recorded almost 10 years ago) -- Bradbury explaining his childhood fascination with the red planet (when he was 10, he stood in his backyard, stretched his hands toward the night sky and called, "Take me home, Mars"); how he first wrote the book as a collection of short stories, (he'd been influenced by Winesburg, Ohio and thought "let's do something for Mars"); weaving them into a novel in 1950 during a spring night in his New York YMCA room, and getting $500 -- his first sale -- from Doubleday that week.

Like Niven's adventures, Bradbury's brief history of his novel is made more interesting, touching and historically valuable because it's in his own voice. Bradbury's reading of the stories themselves, however, is disappointing, precisely because the author isn't an actor. His reading is certainly adequate and enthusiastic and card-carrying science fiction fans will surely want to have tapes of the Master reading his work. Yet given the timeless and haunting quality of tales like "Usher II," "There Will Come Soft Rains," and "The Million Year Picnic," I wanted something more than Bradbury's limited vocal and acting range could offer.

Recorded Books offers an abridged version of The Martian Chronicles read by Leonard Nimoy, an improvement over Bradbury's narration and a nice twist, having the actor-cum-Vulcan reading this seminal work of modern science fiction.

But just think, if you wonder whether writers should read their own works or actors should do the interpreting, what would have happened if years ago an inspired editor had gotten Orson Welles to narrate Bradbury's novel. Ah, then The Martian Chronicles would have been out of this world.