"On the Virginia side of the Potomac he built a mansion in the Georgian style, and named it Laurel House. Here he received senators and Cabinet members, justices and diplomats; the great and the rich, the quick and, had he the power, he would have summoned the dead as well. Even the powerful backwoods politicians . . . gladly discarded demotic trappings in order to go to Laurel House and become, if briefly, a part of that magic circle which was true center." -- Gore Vidal, "Washington D.C."

Life seemed stranger than fiction during a party at Merrywood last night, the Virginia estate that Gore Vidal thinly disguised as "Laurel House" in his book, "Washington, D.C."

"Gore thinks this is as funny as hell," said his half-sister, Nina Straight. "It just caught his imagination. He thinks it's going to be the last chapter of Proust."

The official reason for the Merrywood celebration was Straight herself, a woman with an elaborate family tree, famous connections and an amused eye for Washington.

"I think it's probably the most interesting city in the world," she said. "You don't feel any pressure to be invited to things, but that's maybe because I'm not. There's not too many percentage points to being invited places here, and I guess that's why I've had nothing to do with this guest list. I mean, everybody knows I'll invite my dog."

The party was in honor of Straight's new book "Ariabella: The First." What made it a bit more unusual that the standard publication part is that Straight and Vidal (and Straight's stepsister, Jackie Kennedy Onassis) grew up at Merrywood, and parties like this were as numerous as the servants.

Vidal's novel is not an entirely flattering portrait of Washington political and social life, particularly in his description of Laurel House hostess Frederika Sanford. "A splendid social tactician," he writes of her. h"Not idly had she married for money."

Last night, Nancy Dickerson was the host with Vidal at the Virginia estate, bought by her husband C. Wyatt Dickerson for $650,000 in 1965. His name was not on the invitation, which had furthered gossip column speculation that all was not bliss for him and his wife. But both were there.

"No," said Nancy Dickerson, "we're not getting divorced."

"Does it look like it?" added her husband.

But that was a small matter last night. The real to-do was over co-host Vidal, who hadn't arrived by the time most guests were leaving.

"I love Nini, I love Gore, but I'm furious," said Joan Gardner, a well-tanned guest. "Where is he?"

Severely delayed. At 7:40 p.m., with 20 minutes left in the party that started at 6, he called. "Gore's broken down in Alexandria, and he's taking a Red Top cab!" called Straight to the remaining crowd.

At 8, he arrived. A klatch had gathered near the door.

"He's certainly making an entrance, don't you think?" observed Ina Ginsburg, another guest.

"It was my driver," explained Vidal, who was en route from business in Philadelphia. "He couldn't find Washington. Absolute nightmare."

"Everybody's missed you terribly," said Nancy Dickerson sweetly. "Don't you want a drink?"

He did. While it was being fetched, another klatch of reporters collected around Vidal. One asked him if he didn't feel peculiar to be host of a party in the childhood home he'd written about.

"It's very strange," he said. "Maybe that's why the car was late."

And what of the fictional Laurel House hostess, Frederika Sanford? "Oh, the one who married money," Vidal replied. "Can't think who that would be."

Straight herself spent little time worrying about such complexities. She wore a polka-dot dress, fretted about her upcoming law school finals, and greeted guests from the thin stratum connecting Washington, New York and Los Angeles: Attorney General William French Smith, producer David Merrick, CBS New President Bill Leonard, literary agent Lynn Nesbit, writer Renata Adler, former World Bank president Robert McNamara and Polly Fritchey of old-line Georgetown.

"I love it," said Straight. "I'm not inclined to value-judge a party. I always think of it as a circus." A little later, she added: "I just think it was so nice, I can hardly stand it. I mean helping me sell my book. I guess I'll have to work as the gardener."

Straight grew up at Merrywood with not only Vidal and Jackie Kennedy but also Jamie Auchincloss and Lee Radziwill. It is one of the more confusing collection of well-known siblings, but can be explained, although not necessarily simply, like this:

Gore Vidal's mother divorced his father and married Hugh Auchincloss. Hugh and his new wife gave birth to Nina, who became Vidal's half sister. Then they got divorced. Hugh Auchincloss married for a third time to Janet Bouvier, who had two children -- Jackie and Lee -- from her previous marriage to Jack Bouvier. Jack and Lee became Nina's stepsisters. Then Janet Bouvier and Hugh Auchincloss and Jamie, who is Nina's half brother.

(Q: Now, how is Jamie Auchincloss related to Gore Vidal? See answer at end.)

Straight's book is about a young girl in the rich world of Newport summers, boarding schools and debutante dances. It's not autobiography, said Straight, but "the mood, the texture and the attitude does come back." She is 44, tall, thin and an infectious giggler. Her voice has the tone of East Coast breeding. She has money, three children and an approach that takes nothing too seriously.

"The great thing about my childhood," she said, "was that I saw everything.

Everything was magic. You saw plays, anything artistic . . . But about being among the very rich, I just don't know. I was always sort of on a train [going to boarding school], and I had this little uniform so they would recognize me at either end."

Straight went to Miss Porter's School, then Bryn Mawr and Columbia. She married and divorced former congressman Newton Steers, worked as the Washington correspondent for the Chattanooga Times, then maried Michael Straight, novelist and former deputy director of the National Endowment for the Arts. Now she's going to law school. What all this has done is given her a particularly fine perspective on a city she finds entertaining.

"The great thing about Washington," she said, "is that everyone's accessible. In New York, there are all those tall buildings and people on telephones. In Washington, there's a kind of ebb and flow and mixture."

As for Merrywood, she plays tennis with Nancy Dickerson there. "I probably spend as much time out there as I did when my family owned the place," she said over lunch earlier in the week. "I mean, I'm probably happier out there now than I ever was. Although we had our moments, God knows."

Certainly, she looked happy last night. David Aaron, formerly of the National Security Council, gave his old friend Nina a kiss. "Was it on the lips?" she giggled. "I hope it was."

Then Lorraine Cooper, another old friend, sidled up for congratulations.

"Is the book . . .?" Cooper began.

"Any good?" replied Straight. "No. Just buy lots of it."

Aaron disagreed. "It's just like Nini," he said of the book, "the way it unravels so beautifully."

(A: He's not, at least by blood. "I just call him Gore," said Jamie Auchincloss.)