IF JOHNNY can't read, he's probably got his nose in the kitty litter.

That is, in the voluminous spew of cat cartoons and related gag items clogging the racks at bookstores everywhere. They are not books. They are un-books, and their burgeoning cult has finally become a national embarrassment.

Take Garfield. Please. Anyone who has not been living in a storm sewer for the past two years now knows that Jim Davis' pudgy little feline with the ping-pong-ball eyes is the unchallenged leader in our treacle sweepstakes. All four of Ballantine's Garfield items (the latest is "Garfield Weighs In") is on The New York Times' trade paperback best-seller list. Every frame of every volume has already appeared in Davis' syndicated newspaper strip. Yet at $3.95 each, they have sold collectively nearly 4 million copies since "Garfield at Large" (now in its 23rd printing) arrived, trailing a multi-million-dollar huckster spawn of spinoffs: Garfield toys, board games, T-shirts, calendars, notebooks, coffee mugs, pencils and soap dishes. Two more entries are due in the fall--"Garfield Takes the Cake," and a $7.95 "Garfield Treasury."

Of course, turning cuteness into cash was an American obsession even before we became the first society in human history to dote on a rodent. And no wonder: Mickey Mouse and his zoological cohorts were destined for mass charisma in a nation which supports 60 million household animals and spends more money on pet food than medical research. Soon the U.S. led the free world in the production of cartoon cats. But until 10 years ago, publishers had remained largely aloof. Then B. Kliban's bookstore boom became a gift-shop explosion; supply, cunningly hyped, could create its own demand. The financially feeble publishing industry lurched into catalepsy.

This fact was merely dismal. And perhaps it was not yet absurd, given the mercenary genius of free enterprise, that a moribund second generation, anti-un-books, was foist upon a stupefied nation: "101 Uses for a Dead Cat" (Potter), along with numerous misomammalian entities such as "The Official I Hate Cats Book" (Holt, Rinehart) and "Cat-Haters' Handbook" (Avenel/Crown).

But in the pursuit of Mammon, the race is to the shameless. And the same impoverished redundancy of imagination created yet a third genre: anti-anti-un-books such as "Cat's Revenge" (Wallaby/Simon & Schuster), as well as cognate specimins from "Copy Cat" (Avon), "How to Make Love to a Cat" (Cornerstone/Simon & Schuster) and "How to Live with a Calculating Cat" (Pocket), to "How to Live with a Neurotic Dog" (Pocket) and the apparently inevitable "Pigs in Love" (Potter). A terminal indignity appeared with the recent "dead" and "revenge" versions of other best-sellers. Thus the egregiously successful "The Official Preppy Handbook" (Workman) has its own anti-un-book, "The Joy of Stuffed Preppies" (Owl/Holt, Rinehart); and there's even "101 Uses for a Dead Cube" (Tor/Pinnacle) amid the puzzles and Pac-Men.

There may be some marginal utility to the spate of un-books: If nothing else, they have crowded out that apogee of the human spirit, "A Woman Looks at Men's Buns" (Perigee/Putnam's), a photo collection by a Californian who has the baffling effrontery to identify herself as a "bun-watcher." But by drawing capital, attention and shelf space away from books, and by confounding the young as to what a book really is, purveyors of kitty litter do a disservice to a nation already frighteningly reluctant to read.

A 1978 survey commissioned by the Book Industry Study Group revealed that only 54 percent of adult Americans purchased even one book during a six-month period. Publishers will not broaden that audience by squandering their promotional energies on kitsch, or by aping the clone-a-hit mentality that has made network television a national disaster.

It's time to put the cat out.