Some people couldn't even believe they'd been invited. "The first couple of calls I got," said Nancy Reynolds, the aide who helped arrange Ronald and Nancy Reagan's dinner last night at the F Street Club, "were people who said, 'Are you sure this is serious? It's not a practical joke? I'm a Democrat.'"

But it was serious. Or, to be more accurate, absolutely festive as the Reagans said hello to local Washington in front of a warm fire that crackled under tinkling chandeliers.

"When you come to town," said the president-elect, "there's a tendency as an office-holder to act as if you're a detached servant. Well, I decided it was time to serve notice that we're residents."

A top Reagan aide put it this way: "We want to avoid Jimmy Carter's fatal mistake. He never met the power brokers in this city. He never had any real friends here. Gov. Reagan not only wants to know them, but he needs them to get this place working again."

More than 50 people came to the candlelight dinner, the bulk of them leaders from the city's political, social, religious and sports establishments. Oddly enough, some of them had never met each other, and so the dinner made for some interesting introductions.

"Slava," said National Gallery director J. Carter Brown to Mstislav Rostropovich, music director of the National Symphony Orchestra, "have you met Joe Hirshhorn, the man who provided us with the museum?"

"Ohhhhhhhh," said Rostropovich to Hirshhorn, "that's yours?"

"Nah," said Hirshhorn. "It's everybody's. I gave it to them."

Rostropovich drew closer. "You have such a beautiful face," he said. "Were your parents Russian?"

"Latvian," responded Hirshhorn.

Chuckles all around.

Which was entirely the way the evening went, regardless of your political persuasion. The governors of Virginia and Maryland were there, as were Abe Pollin, owner of the Bullets; John T. Walker, bishop of the Episcopal diocese of Washington; Archbishop James Hickey; Jean Firstenberg, director of the American Film Institute; James Cheek, president of Howard University; Melvin Payne, chairman of the board of the National Geographic Society; Vincent Burke, chairman of the board of Riggs National Bank; publisher Austin Kiplinger, and John Hechinger of the department store.

In fact, the get-together was like a: block party held at the country club, thrown by the new couple who want to make a good impression and get to know the neighbors.

And although people like Ed Meese, who'll be counselor to the president, were overheard arranging what appeared to be transition business for the upcoming weeks, almost everyone else was engaging in well-meaning chitchat about nothing in particular. That, or bending over backwards to be gracious.

Vice President-elect George Bush, for instance, was acting as social liaison between California and Washington, the city he lived in as CIA director and a bunch of other jobs. "Now Ron," said Bush to Reagan, "I want you to meet some people in this community who really make it go -- the Pollins. Wait'll you see the Bullets play."

After dinner, the president-elect told stories over coffee to a captivated audience in the drawing room. Hechinger, Payne, Bishop Walker, Diplomats president Steve Danzansky and Mayor Marion Barry were assembled around him. The fire glowed as outside, in weather cold enough to freeze the prime rate, hundreds of George Washington University students waited for a glimpse of the president-elect.

"Bonzo! Bonzo! Bonzo!" they chanted good-naturedly as he traipsed down the steps after dinner.

Inside, during cocktails, the mayor appeared to be purring like a cream-fed house cat. "This is a great idea," said Barry, who backed Jimmy Carter and had some awfully unpleasant things to say about Reagan until he was elected. "Political rhetoric," he termed it last night. He continued the purr.

So did everyone else in the drawing room, cozy with Oriental rugs and a president-elect who, for the moment, can do little wrong. Now is Reagan's golden age, a honeymoon when he can use good will and his nice-guy style to make his mark on the town.

"Started off well, didn't it?" observed Edward Bennett Williams, the Baltimore Orioles owner and Democrat who's on Reagan's transition team.

"We thought this would be a nice idea," said Nancy Reagan, passing up a spicy cocktail meatball. "We wanted to get to know some people in Washington."

One person she already knew was Nancy Reynolds, the aide and long-time friend who now works in Washington for Bendix Corp. When the two women first saw each other last night, they jumped into each other's arms, hugged for at least a minute, then giggled profusely. Everybody took pictures.

Nancy Reagan was wearing a black knit Adolfo suit with a horizontally striped blouse and it was not, she said, something she'd bought on a shopping trip to New York just hours earlier.

Most everyone else was dressed accordingly, although for something the Reagans had billed as just an "informal" party, people certainly did drag out the furs and jewels. Long, double strands of pearls were popular over silky cocktail-length dresses, which is what you could have found on Barbara Bush, the vice president-elect's wife. The men wore dark business suits and for special snazz, a rectangular "staff" pin on their lapels.

Dinner was at 8:30. The menu, selected by Reynolds with advice from Nancy Reagan: Sherry consomme, veal piccata, salad with cheese, raspberries with vanilla ice cream and champagne. And California wines throughout. There were four round tables with centerpieces of orange and yellow day lilies and two-foot-long candles in silver holders. The napkins and table cloths were white linen, and the place cards were handwritten in an elegant script.

The overall effect, like the F Street Club itself, was of understated old money. Nothing was flashy or trendy.

And liquor was back. One guest, contemplating what was going to be her wine order to the waiter, finally declared: "Oh, make it Scotch and water! The Carters are gone,"

The Reagans didn't arrive at the club until 7:30 p.m., but the hundreds of George Washington students had been assembled on the street outside for nearly an hour. True, a campus poll had Carter winning over Reagan 2 to 1, but Thurston Hall, a freshman and sophomore dormitory, is right across the street from the F Street Club.

So everybody came over with boyfriends and Instamatics for some after-dinner excitement. "I have a class at 7:10 tonight," said Richard Joblove, a freshman from Hollywood, Fla., "but you know, for Ronald Reagan, I guess I can miss it."