A year ago last night, Ronald Reagan's Californians advanced on Washington, taking the city and making it theirs. At close to 100 parties, from Friday cocktails to Sunday dinners, they ate voguish veal and danced in real emeralds. Nancy Reagan shivered lightly in her mink as she stepped from limousine to lunch; Sen. Mark Hatfield (R-Ore.) directed traffic on his doorstep as 400 people came to shake hands with Michael Deaver, the new White House deputy chief of staff. The crowd jammed into the buffet table; waiters had to pass plates through the windows.

"Madness," said a delighted Ted Graber, the White House decorator who had arrived with the Reagans on Air Force One.

"Let Them Wear Adolfos," read the headline in the liberal New Republic a few weeks later.

It was a sharp contrast to the liquorless Jimmy Carter White House, and the Reagans were intent to prove it. Twelve days after the Nov. 4 election, they invited local leaders to a dinner at the F Street Club. The party became a symbol of the switch. As President-elect Reagan himself put it that night: "When you come to town, there's a tendency as an officeholder to act as if you're a detached servant. Well, I decided it was time to serve notice that we're residents."

A year later, Republican insiders are pleased.

"What they really have done," says Robert Keith Gray, the well-connected public relations man, "is recognize that the social side of Washington is an extension of the business day."

But some Democrats are appalled.

"What really shocked me was this Poland thing with Frank Sinatra," says Gerald Rafshoon, Carter's former media man. He was referring to the International Communication Agency's planned television special on the Polish crisis that is to include a song by Sinatra. "Maybe that's what we should have done when the Russians invaded Afghanistan."

Washington's establishment families have another view.

"It seems to me," says Evangeline Bruce, the social doyenne who has had dinner at the Reagan White House, "that it's just the way it's always been -- with the one exception of the Carter years."

"There's a different atmosphere in Washington," says Oatsie Charles, the Georgetown cave dweller who has had Nancy Reagan over for lunch. "They've raised the tone of elegance."

Caterers are growing rich. Black-tie invitations now mean long dresses for women. (Once you could squeak by with a cocktail-length dress for Carter state dinners.) There are a few more flowers in the Great Hall of the White House. And the Watergate has become a roost for "The Group" of Reagan California friends. One of them spent $400 for a lizard bag at Gucci.

But the flamboyant social activity has come during bad economic times. A Washington Post/ABC News poll taken in November 1981 shows that 54 percent of those questioned think President Reagan cares more about serving upper income people than he does the poor, middle class or all groups equally. In February 1981, the same figure was 23 percent.

Some of that can be blamed on the budget cuts and the inevitable disillusionment after a president's first year in office. But the cracks in the decorator wallpaper are showing enough to interest other Democrats, too.

"Their life style obviously presents some political problems for them," says Robert Strauss, the former chairman of the Carter campaign who told Hamilton Jordan and Jody Powell it was important to attend the right parties in town. "It's not that there's anything wrong with it, it's just that it's perceived so poorly. I'd have some advice to give, but I won't give it in the newspapers."

Perhaps more pertinent to an assessment of their social style is the nature of Washington itself. Consider this hypothesis: Washington is one of the country's most socially democratic cities, in that power -- not money and breeding -- get you in. But it's fickle. Like a wintertime California tan that rapidly fades, so does quick glory. Washington might be easy to get, but it's also easy to lose. The superior politician must see a time for caution.

Last summer, after the press had temporarily eased up on its early criticism of Nancy Reagan, her staff complained that it started again. She flew to London for the wedding of Prince Charles, taking with her designer ball gowns and her best friend, Betsy Bloomingdale. She went to 15 social events in seven days, wearing a different outfit to every occasion. She arrived at a polo match with a six-car entourage; Queen Elizabeth drove up a short time later at the wheel of her own station wagon. The British press whooped, "Queen Nancy."

A month later, during the Reagans' California vacation, came news of the rising federal deficit. Now unemployment is close to 9 percent. Last week, on the same day that Washington was stunned by a snow storm and gruesome plane crash, a St. Louis public relations man went ahead with a $30,000 party for Lyn Nofziger, the outgoing White House political director. Meanwhile, Nancy Reagan announced she was giving her designer clothes to museums. The poor waited in cheese lines.

Some senior White House advisers will admit privately that the Reagan social style has its political disadvantages. "All presidents carry some baggage," a top aide sighed several months ago. "This happens to be Reagan's."

In some senses, critiques of the Reagan social style seemed similar to those made of Carter's after his first year in office. At first the Carter style was heralded as refreshing -- people gave grits parties and Jordan wore jeans. But as things reversed politically, it became less fun for the Carter crowd to go out.

The Reagan supporters have not notably retreated from elegance, as last night's parties indicated. But friends say the first lady has felt put upon by criticism for her taste in china, decorating and clothes. She has tried to emphasize her concern for drug abuse rehabilitation.

"It's just unfair to this administration that it was focused in that light," says Peter McCoy, Nancy Reagan's former chief of staff. "The Reagans did nothing more in their entertaining than they've always done."

"The jury's still out on this president," says Strauss. "I sure wouldn't write him off now. With a political figure, things are never as good as they seem to be in this town -- and never as bad. the truth lies somewhere in between."