Washington is a writer's town, primarily a journalist's town, but in recent years, it has become something of a novelist's town as well - and not just for those who became novelists via Watergate. Herman Wouk lives here; so do Larry (The Last Picture Show ) McMurtry and William Peter (The Exorcist ) Blatty. And this year may see the addition of at least three new names to Washington's Famous Authors list.

John Coyne has two novels scheduled to appear in 1979, both of them in the occult, supernatural vein. The Piercing , to be published next month by putnam, mixes religion and the occult in a tale of Demonic possession a la blatty. It's the story of a young priest who, because of an illicit love affair, is exiled to a remote mountain parish where he encounters a young girl who appears to bear stigmata, marks like those Christ received on the cross. In april Berkley will publish Coyne's novelization of the screenplay for The Legacy , an occult thriller to be released by Universal Studios in June and starring Katharine Ross and Sam Elliott. For the original paperback Berkley plans a printing of a million copies and a $300,000 advertising budget.

Friends may be surprised to see the mild-mannered bachelor, who has written nine previous books on sports, crafts and education, writing such gory stuff. "Especially my mother," Coyne laughs. "It works against my character. That's why I purposely chose a picture for the jacket of The Piercing that looked diabolical." But Coyne admits that, "like everyone else, I dreamed of fame and fortune. I wanted a subject that would fit into a particular genre and had great commercial possibilities. There's a reliable market for the occult just like there is for historical romance." The Legacy came about because both Coyne's publisher and Universal are owned by the giant conglomerate MCA. There's big bucks in them thar Hollywood hills.

Barbara Raskin sticks closer to home in Out of Order (due from Simon & Schuster in August), a novel that relates the further adventures of Coco Berman, the zany heroine of Raskin's first novel, Loose Ends . That first novel was published by Bantam as an original paperback and, as such things go, Raskin says, "It didn't hang around too long." But Coco's fans, and Raskin's, did, and the novelist still gets letters from admirers.Her second novel, National Anthem , had an altogether different heroine, but now Coco's back ("People would lke to be like the Bobbsey Twins and go on forever," says Raskin) in what her creator describes as a "comic commentary on various social ills." Coco becomes radicalized "as her small electrical appliances give out and she sees beyond her Sunbeam toaster to the flaws of technology." Ultimately, she is kidnapped by a terroist group "with whom she feels an immediate solidarity." Not surprisingly, several top film actresses have shown an interest in Coco.

A self-described "old Movement groupie," the wife of Marcus Raskin, head of the Institute for Policy Studies and co-defendant in the late '60s with Dr. Benjamin Spock, is well-versed in the ins and outs of Washington politics and media. "Let's just say we were heavily into the '60s," she notes dryly. So heavily that their au pair girl turned out to be a CIA agent.

Fortunately, Raskin says, "the '70s have been very peaceful. I saw the light at the end of two tunnels at the same time - Vietnam was over and my children grew up." The former English teacher and speechwriter for retiring Sen. James Abourezk (D-D.S.), Raskin has continued a career as a free-lance journalist and is a founder and board member of the Washington Independent Writers, an organization "addressing such issues as, What will the publisher do to your book?"

Will there be more stories of Coco Berman? "I don't know what's next," says Raskin frankly. "I seem to be in that early 40s period of re-evaluation."

Washington politics also figures heavily in Susan Richards Shreve's decidely uncomic third novel, Children of Power , scheduled for publication by Macmillan in March. The story follows events during one week in December, 1954, a few months after Sen. Joe McCarthy has been censured by his peers and opinion has turned against him. An alcoholic, McCarthy has been taken in by Sam Taylor, fictional chairman of the Federal Communications Commission, an apolitical man who harbors the senator simply because he is a broken man and a drunk who needs help. The children of the book's title (although their parents are equally important characters) are a group of teen-agers who persecute Taylor's daughter because of her father's link to McCarthy.

Shreve, a small woman who looks much younger than her 39 years, grew up in Washington during the McCarthy era, where her father, Robert Richards, was a prominent journalist and political speechwriter. She now lives around the corner from her childhood home in Cleveland Park and her own children attend Sidwell Friends and St. Albans, schools where her young characters are students. But the novel, she insists, is mostly fiction. "the tone and attitudes are real - it was a time when there was a lack of passion, when people weren't committed to anything, so that it was very easy for them to change their allegiances," says Shreve. "but the story and characters are made-up. Joe McCarthy was reported to be an alcoholic, but I invented some specific incidents that could plausibly have happened."

The novel grew out of feelings Shreve had when she moved back to Washington after a long absence. "It was a difficult time," she recalls. "I felt I hadn't fulfilled the expectations of my childhood and I saw Washington as a metaphor for that. It's a novel about history and responsibility, about the expectations of people who grow up in country with so much possibility. A lot of people, especially here, tend to romanticize the 50's, to see it as a time when dreams were still possible. I have no romantic memory of that time at all."

Because of the recent popularity of novels which feature historical characters - E. L. Doctorow's Ragtime and Gore Vidal's Burr , for example - Children of Power , with alarge cast of characters and a strong plot line, might be Shreve's first commercial success. "maybe for the wrong reasons," she says with a certain hard-earned cynicism. But it is also "a dense novel, a novel of ideas, a novel in which, although the action takes place in seven days, there is a lot of flashback covering 60 years."

Susan Shreve would very much like to make some money, but one gets the feeling she thinks success with critics is more realistic. "What I hope finally," she says, "is I guess what every writer hopes, that this book is advance over the last." CAPTION: Picture 1, Susan Shreve (left) Barbara Raskin, Photographs by Bill Snead; Picture 2, John Coyne