"A Nation of Readers," the exhibit now playing at the Library of Congress, is perhaps less noteworthy for its admirable contents than for its wishful title. Ours is a nation of many things, but "A Nation of Readers" it is not.

Just ask the people in the publishing industry. If there is one thing about which all of them probably would agree--for private if not public consumption-- it is that getting an American to buy and read a book is vastly more difficult than getting a cat to submit to aerosol flea-bombing. A useful and instructive demonstration of the point is to be found in last week's issue of Advertising Age, in which a lengthy article examines the problem of "the mass-marketing of first-rate literature" and finds it to be a thorny one indeed.

The article was provoked by Peter S. Prescott's attack in Newsweek a couple of months ago on the merchandizing of the paperback edition of D.M. Thomas' remarkable and somewhat difficult novel "The White Hotel." Prescott argued that the sales effort--which includes five different covers for the book, "White Hotel" key chains and promotional notepads--was a tacky, demeaning trivialization of "very likely the best novel to appear in 1981." Ad Age's correspondent, blithely abandoning journalistic objectivity, described Prescott's piece as "founded in ignorance and dedicated to elitism," and depicted book publishers as "united in their disgust" over it. Its spleen thus vented, Ad Age got down to the important questions that Prescott's comments provoked:

"How does a publisher market a genuine work of literature without offending the purist or discouraging and frightening away the general reader? How does the mass-market reprinter effect this delicate balance, especially within the framework of the already fragile buyer/seller relationship?"

Behind those questions lurks a single assumption: that the vast, overwhelming majority of Americans does not want to read good books--that the prospect of reading "a genuine work of literature" is "discouraging" and "frightening" to most people. And behind the promotional campaigns for the paperback editions of such "serious" novels as "The White Hotel," "Sophie's Choice," "The World According to Garp" and "The French Lieutenant's Woman" lurks a related assumption: that in order to sell these books in the mass market, the prospective buyer must be persuaded that they are not serious books.

There is nothing new about this. The cover of my 1948 Penguin paperback edition of William Faulkner's "The Wild Palms" shows a woman, scantily clad by the standards of the day, with a beach umbrella in the background; the cover has nothing to do with the contents of the novel and everything to do with catching the reader's eye. Ditto for the 1961 Signet editions of two other books by Faulkner, one billed as having to do with "Sex and Death," the other with "Sin and Redemption." Contrary to the somewhat ingenuous comments of Ad Age, paperback publishers were trying to lure the unsuspecting reader into serious fiction, by hook or by crook, long before the "watershed" success of "Ragtime."

The numbers that constitute "success" are depressingly revealing. In a chart providing a "sampling of top-selling quality paperback books," the biggest success Ad Age can come up with is "One Flew Over the Cuckoo's Nest," with total copies in print of 6.8 million; it has taken 19 years, at an average rate of 358,000 copies a year, to roll up that number. Total copies for "Ragtime" are 3.3 million, for "Sophie's Choice" 2 million, for "The White Hotel" 1.2 million--and these, it should be emphasized, are not total sales but total copies in print, and the difference between the two can be enormous in the mass-market paperback business.

What these figures say to me is that Walker Percy was right when he remarked several years ago that the audience for serious writing in this country is, at best, perhaps 1 percent of the population. Let's put that in italics: at best. Only four "quality" paperback novels have more than 2.3 million copies in print, which is approximately 1 percent of the current population. Most "successful" mass-market paperback editions of "serious" novels are far smaller than that--a couple of hundred thousand copies, perhaps. As for hardcover editions, well, that is to laugh. Hardcover sales are pathetic. It is wonderful news that Anne Tyler's ethereal new novel, "Dinner at the Homesick Restaurant," is a national best-seller, but do you know what that means? At last report, there were 42,500 copies of that novel in print. Another way of putting it is that a copy of "Dinner at the Homesick Restaurant" exists for every man, woman and child in the town of Rockville, Maryland. Period. Spread the population of Rockville around the nation, and it would disappear; that's what usually happens to hardcover books.

Given these realities, it is hardly surprising that paperback publishers are quite willing to resort to just about anything that offers the prospect of enticing people to crack the spines of serious books--serious, that is, by comparison with what usually appears on the best-seller lists. And notwithstanding the objections of my friend Prescott, by and large the publishers are quite restrained in their promotions. When you get right down to it, their gestures in the direction of tastelessness are pretty timid. It may be fatuous and misleading (not to mention condescending) for the jacket of "Sophie's Choice" to proclaim it "A Novel for Everyone," but is it really objectionable? Does it debase a work of considerable literary skill and emotional force? From where I sit, the answer is no. It merely attempts, as one publisher said of the campaign for "The White Hotel," to "coax people into reading on a mass level a novel that normally would have sold 100,000 copies and now maybe will sell 2 million." Ditto for the picture of Meryl Streep on the cover of "The French Lieutenant's Woman," even the steamy kiss on the cover of "Endless Love." This is not exactly the hard sell.

Clear-eyed people in the publishing industry are fully aware that to describe ours as "A Nation of Readers" is fanciful and self-deluding. They know quite well that trade publishing, whether in hard or soft covers, is directed at a minuscule audience even at its most successful. They understand, even if they are uncomfortable with it, that their hard-core constituency is, by American standards, an intellectual elite--and that it is becoming an economic elite as well, as hardcover prices inch toward $20 and mass-market paperbacks toward $5. They know that when they talk, as D.M. Thomas does, of "opening up literature to as many people as possible," they are nonetheless talking small. They just hope they can keep the book business from disappearing into the college bookstores and the English departments, and they know that it is an uphill struggle--that "Sophie's Choice" is "A Novel for Everyone" only in the shrinking world of books.