If you won't judge a book by its cover, you can miss a lot at the Limited Editions Club. Ray Bradbury's ''Fahrenheit 451'' is bound in aluminum. John Hersey's ''Hiroshima'' has a cover of black aniline leather. When production is completed, Gunter Grass's ''The Flounder'' will be accoutered in gray eelskin and Polish linen.
Under the covers, more than acid-free paper and fine letter-press printing awaits. ''Break of Day,'' by Colette, contains three six-color silkscreens and nine drawings in blue and terra cotta by artist Francoise Gilot. Three 12-color lithographs by Larry Rivers will illustrate Isaac Bashevis Singer's ''The Magician of Lublin.'' Robert Motherwell lithographs will appear in a new anthology, ''Poetry From the Spanish,'' edited by Mark Strand. The books are signed by the artist and, when he or she is alive, by the author as well.
Are we talking books here, or are we talking art? Sidney Shiff, who runs the Limited Editions Club, and his son Ben, who designs the books, are eager to explain. This business is an expensive operation, they say, and they are more apt to speak reverently of the ''object'' than of the book.
Founded in 1929 by George Macy and operated by his wife, Helen, after his death in 1956, the club had fallen on hard times by 1978, when Sidney Shiff and three others rescued it. Its membership of 2,000 had dwindled to 500, and outstanding debts nearing $800,000 threatened its demise. With Mr. Shiff running the show, the debts are under control, he says, and there are now about 1,000 subscribers, who pay $750 in advance for 10 books a year. The unattained limit is at present 1,500 members (which is also the size of the usual press run for the titles), but Shiff plans to lower that to 1,200 sometime next year. New members must ante up a richer stake: $1,200 for 10 books. If that sounds like a stiff outlay, the club nonetheless operates in the red, the Shiffs admit.
Overhead is held to a minimum (which a visit to the frightfully plain, sparsely staffed New York City office at 551 Fifth Avenue confirms), but book costs are stratospheric. Varying from title to title, budgets average around $ 100,000 per book to produce those 1,500 copies. The top price for last year's books, if purchased individually from the club, is around $150, but others are often worth considerably more. This year's ''Hiroshima'' is already going for $ 400. Some older issues are even pricier, if they can be found. In 1980, American Book Collector reported that the club's 1934 edition of Aristophanes' ''Lysistrata,'' illustrated and signed by Picasso, was worth $1,400, and James Joyces's ''Ulysses'' (1935), illustrated and signed by Matisse, could be had for were selling for $3,000 three years ago.