A MAJOR growth industry in Washington today seems to be the book-writing business. Politicians are writing slim volumes of poetry; journalists are writing novels, and novelists are writing nonfiction. Senator William Cohen (R-Me.) has published a book of poems entitled Of Sons and Seasons ; reporter Sally Quinn of The Washington Post is writing a novel, and novelist Larry McMurtry has just finished a screen-play about the state of Montana.

Lucianne Goldberg, a New York literary agent who represents Jack Anderson and Kitty Kelley, among other Washington writers, says, "Every major New York publisher needs three or four nonfiction political books each season, and it really doesn't matter whether the books are left, right or center politically. After Watergate it was hard to get someone like Victor Lasky published. Twenty-four houses turned him down before he got printed, but then he stayed on the best-seller list for 26 weeks. The reading public wants political books regardless of what kind of politics they espouse. In terms of the Washington novel, things have dimmed under the Carter administration. If Ted Kennedy wins the presidency, novels about Washington will become important again because the social scene will pick up." w

Despite Goldberg's gloomy assessment of the market for Washington novels, Kitty Kelley just sold Simon and Schuster a Washinton novel called Reunion , which deals with the son of a president who deals dope. Kelley is also reportedly under contract to S&S (for, one hears, a six-fugure sum) to do a biography similar to jackie O! about a woman whose name is still being kept secret. David Richards, the drama critic of The Washington Star , has taken a six-month leave to write a book called The Jean Seberg Story for which Random House paid him a $35,000 advance. Milton Viorst's Fire in the Streets , a history of the '60s, will be coming out in February. His wife, Judith Viorst, continues to write her monthly Redbook column while working on a new poetry book for children. The Washington Post's Metropolitan editor, Bob Woodward, and Post reporter Scott Armstrong's book, The Brethren , reaped a $350,000 advance and paperback rights sold recently for $880,000.

Meanwhile over at the left-wing Institute for Policy Studies, Saul Landau, an IPS fellow, and John Dinges (for six years a Washington Post stringer in Chile) are finishing a book tentatively entitled Assassination on Embassy Row . To be published by Pantheon this spring, their book is based on the killing of Orlando Letelier and Ronni Karpen Moffitt, who both worked at the institute and were murdered by agents of Pinochet's Chilean government.

Writer Taylor Branch and lawyer Eugene Proper -- who prosecuted the Letelier-Moffitt case for the Justice Department -- are also writing a book on exactly the same subject. With $175,000 advance, Branch and Proper say they intend to start writing soon, using Proper as a major character in their version of the assassination story. Branch says that talks are being conducted in Hollywood about filming the still-to-be written story despite rumors of lawsuits against Branch and Proper by Isabel Letelier and Michael Moffitt -- survivors of the two victims.

Clark Mollenhoff is said to be writing a biography of Jimmy Carter. David Horowitz, who recently spent a day at Hickory Hill, and Peter Collier, with whom he wrote The Rockefellers , are getting it together again. Summit Books (an imprint at Simon and Schuster) gave them a $140,000 advance to write a "biggie" about the Kennedys. This puts the two men in competition with Doris Kearns who also writing a Kennedy book for Simon and Schuster, while her husband, Richard Goodwin, writes some of Edward Kennedy's campaign speeches.

Who's writing what about whom in Washington goes on and on and on. The 800 members of the Washington Independent Writers association -- an organization of local free-lancers -- represent only the tip of the authorial iceberg here. Recently WIW has began taking an increased interest in legislation which affects writers' rights. WIW members, finding strength through numbers, are now demanding more rights from their editors and publishers and are negotiating a group libel insurance policy to protect themselves. A legal defense fund has also been established to help pay court costs in precedent-setting cases dealing with writers' rights. WIW contributed $500 to help Gigi Pickford, a member of the organization, establish last July in Small Claims court that a writer's work could not be mispresented as the work of another author.

WIW was also instrumental in founding a national umbrella federation called the Council fo Writers Organizations which represents some 13,000 independent writers from across the country -- a great number of whom are, of course, New Yorkers. COWO -- unlike PEN American Center and the National Book Circle members -- has agreed to participate in the new American Book Awards this spring.

The emergence of several new literary agencies in towns also shows that Washington is viewed as a rich natural resource center of writers. Competing with long established agents like Ann Buchwald are some newer agents like Audrey Adler, who moved to Washington after working at Random House and Dutton. "Publishers are more selective than ever before because the book market is down," says Adler. "They keep asking for well-known people to do autobiographies or for people to write stories about famous people or for social observations about D.C. in either fictive or nonfiction form. New York publishers feel that there's a lot going on here in Washington and they want a piece of the action."

Raphael Sagalyn, of Sagalyn and Welton, Inc., a new literary agency in Washington, agrees. After three years working with the local New Republic Book publishing company, Sagalyn realized that D.C. was a fertile territory for book projects that needed doing. He and his partner "felt that for acquisitions, this town was full of possibility. I think there is very much a literary scene in Washington. The phenomenal growth of the bookstores suggests that Washington is at least one of the most literate of American communities. Compare The Washington Post's and The New York Times' best-seller lists and you'll see widely admired books hold higher positions on the Post list for a longer time. It's only been in the last few years that publishers have begun to tap the huge book potential here," Sagalyn says.

"As an agency we are talking to lots of Washington reporters and journalists who are eager to do fiction because of the financial impetus. Books are becoming front-page news stories now. Judith Krantz and Gay Talese are front-page people. There have been some dramatic changes in D.C. as a cultural center. We are now the media capital of the world, and we're rich in writers and good stories."

Steve Martindale, a Washington lawyer who has branched out into the practice of literary law, says he has sold some 22 books for his clients, among them Liz Carpenter's Hail to the Comic Relief , (bought by Paddington Press). Authors who have little difficulty finding publishers use Martindale's services when it comes to writing contracts to protect the author's interest.

The Howard University Press, which specializes in books for academic and library audiences, has nine new titles for their 1979-80 season. Among these The Wayward and the Seeking: A Collection of Writings by Jean Toomer , edited by Darwin T. Turner, promises to reach a wider audience than usual for a university press. "Such a collection has been long awaited by generations of readers familiar with Cane , Toomer's artistic triumph which instantly made him a major figure of the Harlem Renaissance," says Charles Harris, director of publications from the Howard Univerisity Press.

So literary life in Washington remains lively and highly charged at least in terms of some of the money put up front for promising books by prominent people. Yes, Washingtonians are writing, often about each other, and from the looks of the hefties on this town's best-seller list, they're curled up by the fire on these cold winter nights reading as well.