Siesta Key, Fla. — On any list of today's best mystery writers, the name of John D. MacDonald would have to be in the top few. And why is no mystery. His books sell nearly 7,000 a day worldwide, so either he must be doing something right, or people will buy anything to keep from looking out the window on airplanes. How he can write so prolifically and yet so skillfully makes people wonder if perhaps he has a contract with writer-elves who come in and work nights.
A visit to his substantial yet fanciful up-in-the-air house would make one lean toward the elf theory.
But if you can't believe that, would you believe he works hard? That seems to be the answer. He admits to working 40 hours a week, but simply considering the tonnage of his output - let alone the good quality - his workweek must be nearer 60 hours when he is really at it. He might even be called a ''workaholic,'' but since it is a trite, overworked word, MacDonald would probably reject it. He is a precisian with words.
He lives in west-coast Florida on crowded Siesta Key, but the treetop residence is so ingeniously hidden away it appears to be surrounded only by water, trees, sky, and a few guardian mudholes that must be crossed like shallow moats on the way in from the road.
The fact that he can isolate himself in a crowded area is indicative of his gregarious yet reclusive nature. He likes both people and his work. He likes, but doesn't need, isolation. He could write on a sinking ship, within his invisible walls of concentration. He might even finish a chapter while being carried to the lifeboats.
MacDonald's house he describes as ''up on stilts,'' but it deserves a more substantial phrase. It sits elegantly atop sawed-off telephone poles at a height that enables him to look out at the Gulf of Mexico over the tangle of sea grape and wild shore growth. The porch, nearly two stories up, all but encircles the living quarters. It is full of squirrels and investigating birds, as well as ornamental birds and animals carved of wood, stone, or whatnot.
Once inside the house, a visitor encounters a living room extending perhaps a third of an acre. He is greeted also by a pair of provocative but insouciant cats, which evidently have absorbed a lot of the writer's intrinsic curiosity. (I had only time to remove the camera from its carrying case before the larger cat was getting inside the case to try the flash attachment.) Cats are a constant appendage to his living quarters.
MacDonald fits the house, or vice versa. Both are large, friendly, informal, without pretension. Both indicate, by their style, an appreciative awareness of the world. Both gently exude a relaxed self-satisfaction.
Prolificacy is one of the interesting facts about this man. His fame is mainly in his mystery stories, but he jumped easily out of that mold to write the successful novel ''Condominium.'' He delights readers with his ability to become an expert on almost everything. Even in his mysteries, a kind of textbook expertise on a wide variety of subjects is revealed.
His first novel, ''The Brass Cupcake,'' was published in 1950 without upsetting the literary world. Even those that immediately followed came into publication on tiptoe. It was only by the skill and hard work that distinguish the man that his books eventually gained favorable notice from an eager public and the less eager, slightly surprised critics.
Perhaps the biggest illusion about MacDonald is that he reminds you of a dozen easygoing people you know who live in the next block, or whom you meet at Kiwanis. He is, indeed, a big, six-foot, likable man. But in spite of his easy, friendly manner, he never seems to emerge completely from his inner world. One's impression is that back of his interested eyes is a mental, electronic headquarters where everything is being cataloged. This seeming ability to keep things cooking on the back burner may be part of his secret of success.
When he is wholeheartedly at work, he works on a computer that is impressive in size and sound. The big black boxes fascinate him. They even seem to blend as part of his creative process. While we talked, he coded up chapters of the new book he is writing to show how easy corrections and rewriting can be. He would put a loving finger on the keys now and again, starting it all to whirring, as if the computer was either an extension of him or he of it, and disengagement wasn't easy. It's a creative partnership impossible with a mere typewriter.
His office is a rumpus room of production. It is far from being a mess, but its obvious efficiency is uncharted and unformed. It is full of reference works, manuals on his hobby of photography, disks to feed to the ever-hungry computer, and stacks of in-process writing. The filing system is apparently in his head.
He is an avid editor of his own writing, and writes more than twice as much as emerges at the end. When asked, he says: ''No, I don't know what makes a book sell. I write what I think is a good story and that's it.'' He doesn't admit to being a reformer or a moralist, but he doesn't quite deny it. There is an insistent moral thread running through his books, most often expressed in the philosophical asides of his slightly iconoclastic hero, Travis McGee, but quite often by MacDonald's alter ego, a character known laconically as Meyer. (In fact , Meyer and MacDonald may be almost the same person.)
Writers should have the quality of self-criticism. It is a prerequisite to professionalism. MacDonald has a generous quantity. ''If you want to write,'' he maintains, ''you have to have a split personality; you have to have two sides - one that writes and the other which steps aside and asks: Do I like it, or don't I?'' Firmly built MacDonald doesn't look split, but however he does it, it works.
His books are not prim. He dishes out words here and there that were not felt necessary a generation ago. But compared to other writers, he holds vulgarity in check. His books may not be for everyone, as many contain explicit sex and some violence.
His protagonist, Travis McGee, is big, fortyish, ruggedly handsome, and adored by women, most of whom are in trouble. And afterward, grateful. His villains are usually offbeats: antisocial, psychopathic, unprincipled scoundrels. There is no thin line between the good and evil. Getting the bad guys is what it is all about, and Travis McGee does just that - sometimes with violence, sometimes skirting the law - but he settles things in traditional form. MacDonald feels strongly about ''good'' without being didactic. ''The primary sin,'' he says, ''is hurting people for no reason.''
There is a debate among Travis McGee fans as to why all his mystery titles include a color - for example, ''The Long Lavender Look,'' ''Dress Her in Indigo ,'' ''The Girl in the Plain Brown Wrapper.''
Earl Stanley Gardner, it was said, was slightly superstitious about the titles on his Perry Mason series, so he imitated the form and lilt of the title that first gave him success, such as ''The Case of the Blonde Bonanza,'' or ''The Case of the Cautious Coquette.'' So some believe MacDonald follows this pattern. It is probably not true. One possible explanation is that the titles are color coded; the color plays a part in the story. Although this is factual, it isn't convincing; the color is not all that important to the plot.
A better explanation may be that the color-scheme titles are a nod toward promotion. It is an identifying mark of a Travis McGee mystery, and thus makes it stand out to a mystery buff.
Mystery stories have been intensely popular ever since the advent of the most famous private eye, Sherlock Holmes, and mystery fans continue to be a loyal, enthusiastic audience. Some bookstores say that mystery sales run steady even when times are hard. As one woman, recently out of a job, put it: ''I'll buy cheaper food, I'll wear cheaper clothes, but I still want first-class mystery stories.''
A debatable set of priorities, no doubt. One worthy of Meyer, Travis McGee, or perhaps John D. MacDonald himself.