EVERY ONCE IN A SHORT WHILE I GET a letter from some eager young would-be writer asking me for some "hints" on the art of writing science fiction.

The feeling I have is that my correspondents think there is some magic formula jealously guarded by the professionals, but that since I'm such a nice guy I will spill the beans if properly approached.

Alas, there's no such thing, no magic formula, no secret tricks, no hidden short-cuts.

I'm sorry to have to tell you that it's a matter of hard work over a long period of time. If you know of any exceptions to this, that's exactly what they are-exceptions.

There are, however, some general principles that could be useful, to my way of thinking, and here they are:

1) You have to prepare for a career as a successful science fiction writer-as you would for any other highly specialized calling.

First, you have to learn to use your tools, just as a surgeon has to learn to use his.

The basic tool for any writer is the English language, which means you must develop a good vocabulary and brush up on such prosaic things as spelling and grammar.

There can be little argument about vocabulary, but it may occur to you that spelling and grammar are just frills. After all, if you write great and gorgeous stories, surely the editor will be delighted to correct your spelling and grammar.

Not so! He (or she) won't be.

Besides, take it from an old war-horse, if your spelling and grammar are rotten, you won't be writing a great and gorgeous story. Someone who can't use a saw and hammer doesn't turn out stately furniture.

Even if you've been diligent at school, have developed a vocabulary, can spell "sacrilege" and "supersede" and never say "between you and I" or "I ain't never done nothing," that's still not enough. There's the subtle structure of the English sentence and the artful construction of the English paragraph. There is the clever interweaving of plot, the handling of dialog, and a thousand other intricacies.

How do you learn that? Do you read books on how to write, or attend classes on writing, or go to writing conferences? These are all of inspirational value, I'm sure, but they won't teach you what you really want to know.

What will teach you is the careful reading of the masters of English prose. This does not mean condemning yourself to years of falling asleep over dull classics. Good writers are invariably fascinating writers-the two go together. In my opinion, the English writers who most clearly use the correct word every time and who most artfully and deftly put together their sentences and paragraphs are Charles Dickens, Mark Twain, and P. G. Wodehouse.

Read them, and others, but with attention. They represent your schoolroom. Observe what they do and try to figure out why they do it. It's no use other people explaining it to you; until you see it for yourself and it becomes part of you, nothing will help.

But suppose that no matter how you try, you can't seem to absorb the lesson. Well, it may be that you're not a writer. It's no disgrace. You can always go on to take up some slightly inferior profession like surgery or the presidency of the United States. It won't be as good, of course; but we can't all scale the heights.

Second, for a science fiction writing career, it is not enough to know the English language; you also have to know science. You may not want to use much science in your stories; but you'll have to know it anyway, so that what you do use, you don't misuse.

This does not mean you have to be a professional scientist, or a science major at college. You don't even have to go to college. It does mean, though, that you have to be willing to study science on your own, if your formal education has been weak in that direction.

It's not impossible. One of the best writers of hard science fiction is Fred Pohl, and he never even finished high school. Of course, there are very few people who are as bright as Fred, but you can write considerably less well than he does and still be pretty good.

Fortunately, there is more good, popular-science writing these days than there was in previous generations, and you can learn a great deal, rather painlessly, if you read such science fiction writers as L.

Sprague de Camp, Ben Bova, and Poul Anderson in their nonfictional moods-or even Isaac Asimov.

What's more, professional scientists are also writing effectively for the public these days, as witness Carl Sagan's magnificent books. And there's always Scientific American.

Third, even if you know your science and your writing, it is still not likely that you will be able to put them together from scratch. You will have to be a diligent reader of science fiction itself to learn the conventions and the tricks of the trade-how to interweave background and plot, for instance.

2) You have to work at the job.

The final bit of schooling is writing itself. Nor must you wait till your preparation is complete. The act of writing is itself part of the preparation.

You can't completely understand what good writers do until you try it yourself. You learn a great deal when you find your story breaking apart in your hands-or beginning to hang together. Write from the very beginning, then, and keep on writing.

3) You have to be patient.

Since writing is itself a schooling, you can't very well expect to sell the first story you write. (Yes, I know Bob Heinlein did it, but he was Bob Heinlein. You are only you.)

But then, why should that discourage you? After you finished the first grade at school, you weren't through, were you? You went on to the second grade, then the third, then the fourth, and so on.

If each story you write is one more step in your literary education, a rejection shouldn't matter.

[Editors don't reject writers; they reject pieces of paper that have been typed on. Ed.] The next story will be better, and the next one after that still better, and eventually But then why bother to submit the stories? If you don't, how can you possibly know when you graduate? After all, you don't know which story you'll sell.

You might even sell the first. You almost certainly won't, but you just might.

Of course, even after you sell a story, you may fail to place the next dozen, but having done it once, it is quite likely that you will eventually do it again, if you persevere.

But what if you write and write and write and you don't seem to be getting any better and all you collect are printed rejection slips? Once again, it may be that you are not a writer and will have to settle for a lesser post such as that of chief justice of the Supreme Court.

4) You have to be reasonable.

Writing is the most wonderful and satisfying task in the world, but it does have one or two insignificant flaws. Among those flaws is the fact that a writer can almost never make a living at it.

Oh, a few writers make a lot of money-they're the ones we all hear about. But for every writer who rakes it in, there are a thousand who dread the monthly rent bill. It shouldn't be like that, but it is.

Take my case. Three years after I sold my first story, I reached the stage of selling everything I wrote, so that I had become a successful writer. Nevertheless, it took me seventeen more years as a successful writer before I could actually support myself in comfort on my earnings as a writer.

So while you're trying to be a writer, make sure you find another way of making a decent living- and don't quit your job after you make your first sale.