FIFTY MILLION COPIES of his 29 novels have been sold worldwide, and the 30th, Western, is being published this month. His mother spanked him, he says, when he was a child because he was continually making up stories, but readers in a dozen languages have reason to be grateful her discipline didn't stick. "A writer who has no audience isn't much of a writer," says Georgia-born Frank Yerby, speaking from his home on the outskirts of Madrid, where he has lived since 1956. Part black, part Scotch-Irish, part American Indian, he explains his expatriation in a voice that still has a definite southern flavor: "I had one solution to the racial problems of the United States -- I bought an airline ticket." But his flippancy is a mask for old wounds that must still smart, and three of his books have featured black protagonists. However, he rightly insists, you can't judge books by their color.

In 1946, before Yerby left America for Europe, Dial (with whom he has remained for the entirety of his career) brought out his first novel, The Foxes of Harrow. Before that he'd published poetry and a short story in Harper's that won an O. Henry prize. Actually, Yerby confides, Foxes wasn't his first novel, strictly speaking. "I wrote a horrendous proletarian novel of the type that was being done then, about a prizefighter who worked in the steel mills and had a tragic life. I sent it in to a Redbook fiction contest." An editor, though rejecting the manuscript, did give him hope: "This is godawful," Yerby says he was told, "but you can write."

And so he determined to try again. The Foxes of Harrow, set in the 19th-century American South, "has a coin in it that hadn't been minted yet and one character shoots a pistol before that gun was invented," Yerby chuckles. But that didn't stop it from selling 485,000 copies and becoming a movie with Rex Harrison and Maureen O'Hara. Now, with subsequent novels set everywhere from the Great Plains to medieval Spain, Yerby pays more attention to his research, doing much of it in the languages most readily available to him, French and Spanish.

A typical Yerby plot seems to involve a strong man who has to choose between two women, and there usually are more-than-generous helpings of revenge, madness, suffering and violence. It's a formula he's mastered, and he believes he sells "because one has learned one's craft and does one's job." Of his own work, Yerby's personal favorites are those he says no one else likes. An Odor of Sanctity (1965) is one he names, as well as The Dahomean (1971) and The Garfield Honor (1961) -- this last being, he claims, "an accurate western, with no Hollywood legend allowed to creep in."

Himself, he eschews reading in his own genre, historical fiction, but enjoys other escapist fare, like spy stories and thrillers. Also, he confesses, "I take the keenest pleasure from absolutely terrible novels, the ones that are so bad they're good." It's obvious, however, that Yerby derives much pleasure from his own iconoclasm, and, if over the years, he's gotten knocks from "serious" critics, he's willing to knock back. His academic background (he took a master's in English and later left a doctoral program at the University of Chicago to teach in the South) shows when he proposes that members of any "literary establishment should be condemned to read English Bards and Scotch Reviewers each morning."

His 31st novel, Devilseed, "about the most outrageous female since Moll Flanders," is already delivered to Dial, and Yerby is starting to think whether or not he will base his 32nd on the little-known St. Patrick's Brigade, "some 300 Irish-Americans who deserted to Mexico during the Mexican-American War." His staying power and his imagination are keeping pace, and he's well aware that while popularity and respect often diverge the former is hardly a curse. "Thackeray," he reminded "Book Report" drily, "didn't starve."