There was this party last week at a Bethesda restaurant, given for a departing Washington newsman and attended largely by newspaper people. Everybody was preoccupied, exchanging bits of news and gossip when, suddenly, the noise level in the room dropped noticeably and all eyes focused on a just-arrived guest. A slight hissing actually could be heard.

The object of everyone's attention was William Safire, The New York Times columnist and former Nixon speechwriter whose first novel, "Full Disclosure," about a President who goes blind in office, had just been auctioned off among paperback houses for an astonishing $1,375 million.

The sum is not only a record for a first novel but the latest incredible financial height reached in the increasingly passionate buying and selling of Washington novels. Leading up to the Safire stratosphere were, to mention a few, Barbara Howar's "Making Ends Meet," which sold for $800,000; Les Whitten's "Conflict of Interest," $360,000, and Patrick Anderson's "The President's Mistress," $250,000, Spiro Agnew's "The Canfield Decision" and John Ehrlichman's "The Company" also sold for huge amounts.

Safire, when yeached was taking a previously planned long weekend in Acapulco ("He's off spending some of the money he hasn't gotten yet," suggests a colleogue at the Times' Washington bureau's), says that "all the ribbling has been goodnatured." Safire, himself, tried to make light of it saying, "Nobody picks up a check anymore."

But if he was "flabbergasted" by the sale - "I went home and told my wife and she didn't believe it. I tell you the truth, I don't believe it myself," - so are a number of his acquaintances. While Safire sunned himself, others were left behind to ponder the meaning of a $1,375 million sale.

"Watergate put Washington on the map as a center of intrigue," says Les Whitten, who believes there were more writers doing Washington novels in the early '60s when he began. It's just that nobody cared as much then.

"It's the power," adds a leading Hollywood director, reflecting film-makers' perception of Washington as a center of fascination and glamor. Hollywood promoters are fantasizing about a "Roots-like impact" from "Washington, D.C.," the television film now being produced from Ehrlichman's Watergate novel.

Certainly the Washington novel is nothing new. The roman-a-clef guessing game has been going on here at least since 1880 when Henry Adams published "Democracy," a novel in which the bumbling President resembled Ulysses S. Grant. Allen Drury's "Advise & Consent" came out in 1959. And Fletcher Knebel grabbed attention in the 1960s with his "Seven Days In May" and other thrillers. Then came Watergate.

"There's much more interest in Washington and things about Washington," says Hillel Black, senior editor of William Morrow. "It dates to, among other things, Woodward and Bernstein; Watergate, really, and the drama that came out of it. "The Final Days' had a great impact."

"The Final Days" ranked as the top non-fiction seller in 1976, followed by three other Watergate-related books in the top 10. Publishers and agents say Washington novels feed the Watergate-provoked interest in behind-the-scenes government machinations and in the personal lives of Washington figures.

"More interesting than Adam or Eve," says Hillel Black, "is the snake." pointing to the seamy, and alluring, underside of Washington life "There's also a positive aspect to it, too. Our institutions did survive at a critical period. Washington provokes distrust, dislike and admiration."

There are other factors in the saleability of Washington novels. It helps, for example, to have a widely recognized name resulting in what Patrick Anderson calls "the celebrity novel . . . Novels sell because the author gets on national television."

"There's a much higher interest in a first novel by a notorious or well-known person than, say, the fifth novel by a very respectable novelist," says Scott Meredith, the agent for Agnew's novel, which landed on bestseller lists despite poor review. "There's a special curiosity value about it."

Safire can claim such "celebrity" status on the basis of his Times and Nixon credentials. In addition, Safire offers his publisher another asset: Doubleday publicist Olivia Blumer describes him as "a very professional promoter."

Blumer says she observed him promote his massive Nixon chronicle, "Before The Fall." (Safire likes to point out that the paperback sale after Nixon fell was only $5,000 and that he believes people view his new success in the context that things have a way of averaging out.")

"I learned more about promotion from Safire than anybody else." Blumer says. "I just came into the touring department when he did Atlanta and Chicago. He knows Washington. He answers questions concisely. He'll help an interviewer who may not be too good."

And what is it precisely that makes Washington novels so appealing.

"It's the glamor locale," says Scott Meredith.

Safire says "It has to do with power, and what it does to people and what they do with it."

Whitten cites the "sexiness of newspaper reporting" and "political murders" that make up many new novels. He says agencies such as the FBI and CIA provide ready-made drama.

Whitten says of his "Conflict of Interest" offers an "authentic Washington background" because he's lived here most of his life, and that it offers, he says thanks to his editor, the proper "pace." Literary agent Ann Buchwald ways a common failing of Washington novels is that they "get bogged down with what the writer is steeped in."

Naturally, a good title helps. Patrick Anderson has a winner in "The President's Mistress." He wanted to call it "Affairs of State" but was talked out of it by his editor at Simon and Schuster, Michael Kerda. Anderson also credits Korda with the idea for the book.

Finally, one must keep his mind on the sale of the book while writing it if a blockbuster of a sale is the object. "With my first two books my goals were much more literary," sais Anderson. "This one was always conceived as a commercial novel." He can live with this fact of life partly because the paperback rights to one of his earlier books has been sold as a result of "The President's Mistress."

Everybody from spy master John Le Carre to Elizabeth Ray seems ready to write about Washington. Le Carre is said to be thinking about relocating here for a time while collecting Washington-based material for part of a novel. As for Ray, who already has produced the roman-a-clef "The Washington Fringe Benefit," Scott Meredith says, "She's talked about a plot with a member of my office. He keeps sending her away saying it's not strong enough. She keeps coming back with improvements."