The Eagles flew into town last night, flapping their furs, flashing their diamonds, and reaffirming their faith one year to the day in Ronald Reagan's "New Beginning."

To become an Eagle, one must contribute at least $10,000 a year to Republican National Committee causes. They are the Party's status birds. Last night, Learjets and shiny limousines brought them to Washington for their annual dinner, which was scheduled to coincide with the first anniversary of the Reagan inauguration.

"This is a very impressive gathering," said the president, surveying the crowd at the Washington Hilton. "When I walked in I thought I was back in the studio on the set of 'High Society.' "

President and Mrs. Reagan, Vice President and Mrs. Bush and most of the Cabinet showed up. A coup by any standards.

"Everyone here is important," Richard Richards, chairman of the RNC, told the crowd.

Importance didn't come cheap. The 200 tables, which each seated about 10 guests, went for a minimum of $10,000 apiece. And just about everyone went home happy. The RNC cleared $2 million and guests got fruit cup, filet mignon, conversation with prestigious Washington officials and a jar of Jelly Bellies for the road. Still, there was the occasional dissenter.

"Actually, I think this whole thing is rather ridiculous," said one woman in flowing pink chiffon. "I mean the country's in a recession and on the first anniversary we're all here throwing away thousands of dollars . . . Of course I won't give you my name; I'm not crazy." The pink chiffon fluttered away into the black velvet and glitter.

Oh, what a sea of Adolfo, Galanos and Bill Blass!

Nancy Reagan wore a black sequined off-the-shoulder Galanos gown with a huge beaded silver star across the front.

Socialite Nancy Dickerson wore a black beaded Bill Blass with fuchsia and red sequined stripes across the front.

"It used to be Bill Blass'," Dickerson said. "But it's mine now, unlike some people I read about."

Socialite Ruth Buchanan was wearing her taffeta and sequined Adolfo. "I just got back from Main Chance, where I lost weight," she said, "and now it doesn't fit me."

Secretary of Transportation Drew Lewis wore a tuxedo and a neckbrace. He pinned his bow tie to the brace. "The bow tie was my wife's idea," said Lewis. "She took one look at me tonight and said, 'Boy, do you look stupid.' " Lewis tripped and fell outside his Watergate apartment a few days ago.

The guests came from Palm Beach, New York, Dallas, Palm Springs, Los Angeles.

And Baltimore.

"I think we're definitely worse off than we were a year ago," said Lindsay D. Dryden III, 36-year-old CEO of Dryden Oil. He calls himself "Trip." "I think it's Reagan's economic policy. He's trying to cut back in spending, but the biggest sacrifices are being made by business. We're making half the profit we made a year ago."

The bottom line seemed to be on most people's minds last night.

"I'm not here just to wear a black tie and socialize," said Richard Berendzen, president of American University. "This is a challenge for me tonight. There are a lot of people here who can provide private support for schools. If the federal government is cutting education programs, who else is going to make up the difference? We're worried."

From the dais, Richard M. DeVos, RNC finance chairman, asked: "Are you as confident tonight as you were a year ago?"

Answer from the crowd: weak applause.

The politicians were not much more encouraging. But they tried harder.

"Yes, there is a recession," said the president, "but it didn't start a year ago tonight."

"We're better off now than we would have been if Jimmy Carter had been elected," said Rep. Jack Kemp (R-N.Y.), a flag carrier of Reaganomics. "The economy was in chaos. Now we just have to get rid of the Fed policy. It's irrational and volatile. Paul Volcker thinks recession cures inflation and he's wrong."

"If interest rates don't go down, we're in real trouble," concurred Secretary of Health and Human Services Richard Schweiker, adding that he was also "critical" of the Federal Reserve Board's policy. But basically, the evening wasn't all that serious.

In between bites of tropical fruit sprinkled with bits of coconut, guests listened to Marie Osmond sing "God Bless America" and danced to the Lester Lanin Orchestra, which played big band music. He's the Reagans' favorite. The president and Mrs. Reagan smiled and clapped but didn't dance.

And despite some grumblings, the president and vice president were only upbeat.

"I like my job," said an enthusiastic George Bush.

"In case you've wondered," Ronald Reagan told the crowd, "Nancy and I are happy in our work."