You may qualify for the book-writing life if you can . . .

Be selfish

Stand it if your mother doesn't read your books

Put up with insults from non-writers

Not speak to your family for 12 straight hours for days on end

Believe you can write as well as Truman Capote, at least sometimes

Write before breakfast

Few life styles are more envied than that of the author. Yet his elevated status appears-under close scrutiny-to be a long series of agonies punctuated by an occasional (and usually very dangerous) moment of ecstasy.

Sitting down to write a book carries with it all the risk of Evel Knievel's Snake River stunt, except that the author is not equipped with a parachute.

Deadline worry and self-discipline are among the least of the author's natural hazards. One must be prepared to turn the wrench on all usual behavior patterns and become supremely selfish. This worship of privacy can make the author seem despicable at times, if not wholly mad.

Nobody really understands the writting life except those are leading it, but one bedeviled author with a bookj in progress can invariably spot another. There's something funny going on behind the eyes . . .

"What separates writers from all other artists is that writers really don't want to write," says Merle Miller, who has written nearly a dozen books and countless screenplays, television treatments and articles.

"Lok at it honestly," he says. "Caslas played Bach before breakfast. He couldn't wait to get to his cello. My friends who sculpt and paint can't wait to get to their sculpting and painting each day. Conductors love to conduct and actors love to act, once opening night is over.

"But writers-I have never known a writer who does not view wach day as execution day because he must sit down and write. Musicians speak to each other of the joy they derive from their work. Writers speak to each other of the pain, the terror and the trepidation. That's why writers drink so much."

Miller, now completing a large volume on Lyndon Johnson (which follows "Plain Speaking," his oral history of Harry Truman), complains that while most authors can comfort themselves with the knowledge that at least their mothers will like what they write, "Mother doesn't even read my books. She is always telling her friends, 'Merle hasn't had steady work since left Harper's in 1950.'"

But it's not just the writing that bedevils writer. "It's what you have to do to yourself and to your family just in order to write," says Frank Mankiewicz, president of National Public Radio and author of six books, the most recent, "With Fidel" and "Remote Control."

"You must instruct your family to stay away from you, not to come near you, not to speak to you. And if you should wander out of your den and attempt to speak to one of them, they must be trained not to answer you. You are to be ignored."

A further hazard of the writing life:

"If you smoke at all," says Mankiewicz, "you'll be smoking three cigarettes at once by the end of the book. Since I've quit smoking, I've probably also quit writing."

CBS commentator Rod MacLeish, author of "The Man Who Wasn't There" and four other books, says, "It takes years to cave into your own work habits and it takes even longer to get tick-skinned about the frustration of writing two or three things at once.

"For instance, I was writing a book about Washington politics, 'A City on the River,' which was to come out before the 1972 election. At the same time I was writing newspaper pieces and doing radio commentary. I developed a tapioca a mind and sometimes went into a total 'mental numb.' But I had to finish that book on time, and I did. And what happened? They brought it out eight months after the election."

The inability of authors to control publishers' foot-dragging and strange whims is one hazard of book-writing, according to MacLeish, but he also would warn the fledgling author about selection of subject matter.

"The Man Who Wasn't There' was a novel about a man being driven insane. I got a call from a guy in Idaho who said he'd read my book and that I'd stolen his life story. "They're been driving me insane for years,' he said. 'I want a check for $9 million right now or I'm taking you to court.'"

The moral, says MacLeish: "If you write a novel about fruitcakes, you will hear from fruitcakes."

Michael Mooney, a contributing editor to Harper's and author of "The Hindenburg" and the upcoming "Memento," states flatly that the writing life is nothing less than "perilous."

"If you write a book," says Mooney, "it is guaranteed that the IRS will appear and audit your tax returns. Further, your must be prepared to be sued by a lawyer who has diligently searched for a client who might be prepared to allege that you have libeled him, invaded his privacy or committed a copyright violation.

"The cost of defending the suit will exceed all possible royalties earned. But the suit will not appear until two to four years after publication because it will take the lawyer that long to find someone who is supposedly injured by your book."

Washington books are particularly perilous, warns Mooney, "because if you should happen to mention in your book that the president or a cabinet officer is a damn fool or a nut, an intelligence file will be started on you.

"Someone will be assigned to copy the return address of everyone who writes to you first class. But this has one possible benefit: If you can find the person who was charged with this dreary task, you will have one dandy and complete Christmas card list."

Another freakish by-product of authorship is the rather whimscial brand of hostility practiced by total non-writers upon full-time writers. All manner of inexperienced folk will say unabashedly, "Now, when I write "my' book . . ."

The same folks would never say, "Wait until you hear my oratorio," to Leonard Bernstein, or "When may portriat is unveiled . . ." to Jamie Wyeth.

Why are authors fair talk and occasionally make themselves vaguely understood, they think they can also write; they think it's the same thing," says Merle Miller. "They secretly believe that the published writer is probably some kind of a trickster and they want to make him feel guilty.

"Unfortunately, writers tend to believe this themselves and are apt to feel guilty about being paid for what they do. The only people who will ever tell you 'I can't write' are writers and usually very good ones."

"If they are not quite certain they can write," says MacLeish, "they sure as hell know they can edit, and do. Every man an editor."

Mooney believes that good writers allow themselves guilt because of the self-starting lies they must begin with.

"A writer has to believe that he is at least as good as Herman Wouk all the time and almost as good as Truman Capote or Gore Vidal some of the time," he says. "Writers have to think they can write three times each day, every day, the equivalent of one newspaper column, which adds up to about 90,000 words in all.

"You have to tell youself you can do this in order to keep going, which is of course very hard since it is impossible and you know it."

The writing life is hazardous indeed. And all wistful would-be authors should take heed: A book is not a series of articles strung together against a faraway deadline. A book is a separate lifetime, a great fire-breathing dragon to be slain.

There is only one sure way to know whether you can and should take it on: Because you must. CAPTION: Picture 1, Merle Miller; Picture 2, Michael M. Mooney; Picture 3, Rod MacLeish; Picture 4, Frank Mankiewicz