It is a mighty tribal rite. Each new administration in Washington must select a haunt to call its own, a place to drink Scotch and eat trout, influence and inform, gossip and -- perhaps most crucially -- be gossiped about. In short, the "in" spot for the "in" crowd.

The Carter White House drank at Sarsfield's, or at least they did until Hamilton Jordon allegedly spewed Amaretto on a young lady near the bar. The Kennedys discovered Sans Souci, the Washington noontime institution that was in, out, then in again. Now it's been taken over at lunch by the Federal City Club and thus, removed from the running.

In the fledging Reagan era, there are two spots, one old and one new, that have emerged as early hangouts. It's the Class Reunion for drinks, Maison Blanche for lunch.

There's clear evidence. At "The Class," as you're supposed to call it, the Republican end of the bar looks like Detroit, July 1980. And at Maison Blanche, grazing contently at table 14, you can find that true barometer of lunchtime chic: columnist Art Buchwald, refugee from the "Sans."

"Wherever I eat lunch," he decrees, "is the in place." Maison Blanche

Lunchtime, yesterday. "Ordering one floundarrrrre," sings the chef, his French accent as delicious as the scent of butter and garlic. "Ordering one shad roe. Ordering two scallops du jourrrr. . ."

Outside the swinging kitchen door are dark leather banquettes, twinkling chandeliers and shiny, technicolor pastries. The place is big and bright, with tables spaced too far for effective eavesdropping. But people manage.

At the same time, waiters scamper and wine corks gently burp. Eyes turn from plates to door, determining what famous person is walking in next. With each new sighting, the diner feels delightfully smug. What savoir faire to find an in place -- and slightly ahead of the crowd.

Here's who's been in lately:

Presidential counselor Edwin Meese. White House Chief of Staff James Baker, dining three weeks ago with Michael Deaver, deputy chief of staff. (That really put the place on the map.) CIA Director William Casey. Barbara Bush, wife of the vice president. Ethel Kennedy, despite political affiliation. Attorney General William French Smith. Henry Kissinger with former national security adviser Zbigniew Brzezinski. (Everyone in the place murmered.) White House political director Lyn Nofziger. "I don't go there to see and been seen, my dear," he says. But he does go a lot.

Yesterday at lunch, CBS' White House correspondent Lesley Stahl arrived, press tags dangling from her neck. She spotted a photographer near the door. "Don't take a picture of who I'm having lunch with," she said "because it's really an affair."

Stahl is easily recognizable to the staff at Maison Blanche, but some of the new stars of Washington officialdom tend to look alike. Or at least they do to a staff that recently seated the secretary of defense after referring to a crib sheet.

It's carefully hidden under the payroll records at the maitre d's stand: a newspaper page full of pictures and biographies of the new Cabinet and senior White House staff. "I think the only time I looked at it," says co-owner Anne Hartley, "was for Caspar Weinburger."

Once Martin and Annelise Anderson were there on the same Friday, but at separate tables and unbeknownst to each other. He's the president's domestic policy adviser, she's an associate director at the Office of Management and Budget. Martin Anderson got up from his lunch with Lesley Stahl (he wasn't the gentleman in question yesterday), sped for the door, but was then informed his wife was nearby.

"Say hi to her for me," he said. "I'm late. I gotta see the president in two minutes."

Even some familiar Democrats have started hanging around the place. Not too long ago," Dinah Shore was given a "Welcome to Washington" lunch by Orioles owner Edward Bennett Williams, Buchwald, lawyer Joe Califano, Jack Valenti of the American Motion Picture Association and George Stevens of the American Film Institute. "Whenever she comes we welcome her," says Califano. When the $120 bill came, the table held an election to determine who'd pay. Buchwald won, chuckles Califano, who lost.

"What else is new?" says Buchwald. "If Califano paid, that would be a news story."

There are other Washington lunch spots, Mel Krupin's in particular, that attract the Reagan White House. But Krupin, the former manager at the original power lunch spot, Duke Ziebert's, appears to pull a few more democrats. And besides, Maison Blanche has the geographic advantage of being one block from 1600 Pennsylvania Ave. It's pronounced "Mayzon Blonsh," and means White House in French.

"We didn't do anything," says Tony Greco, the owner, "we just happened to be across the street." Perhaps he has simply forgotten the ad his restaurant placed in a local magazine that describes it as attracting "famous legislators, foreign dignitaries and other celebrities."

What makes a restaurant like Maison Blanche suddenly "in his less to do with its generally accepted good food and service and more to do with the peculiar nature of Washington itself. In this case, the temporary power vacuum after the last election created the usual mass insecurity about where to go. But then, slowly, high-profile White House reporters began having lunch with transition sources there.

After Jan. 20, those sources became White House celebrities. And after that, word-of-mouth and gossip columns did the rest. Where Meese, Baker and Deaver go, so goes the nation's capital.

"That's incredible," says Baker, informed that he's helped create a Washington "in" spot. "I just like the food, and it's easy to get to."

Maison Blanche opened in the Federal Home Loan Bank Board building in January 1979. At first times were rough.They suffered from a bad review, the tucked-away spot on F Street and Jimmy Carter's campaign against the "three martini lunch." But a year ago, the reviews improved. And on Nov. 4, the neighbors switched to Republicans who knew a truffled chicken ($13) when they politely tackled one. And perhaps more important: They could pay for it without guilt.

"I don't think the Carter administration was into French cuisine," says Greco, the restaurant mogul who has helped build and finance places like Rive Gauche, Tiberio, Le Bagatelle, The Big Cheese and Le Steak. "To tell you the truth, I voted for Reagan. As far as business was concerned, the restaurant industry was down during the four years of the Carter administration. Now it's expanding, and much improved over last year."

People like Bill Casey have helped. Greco recalls that the CIA director came to him just prior to the inaugural, anxious to have a private party at the restaurant. Only problem was, Greco didn't recognize him.

"I didn't know who this guy was, okay?" he says. "So he comes in, and I sit down with him, and he wants a party on Sunday -- and this was Wednesday. For about 50 people. Well, we're not open Sunday, so I offered him my house."

After some more discussion, Greco decided to open the place just for Casey. But the next day, Casey canceled. Only then did Greco find out who he was.

"Gee," he says, "it seemed kind of weird that I'd be entertaining the CIA director in my house."

Lunch and wine for two at Maison Blanche goes for about $40. You can have veal chops with mushrooms, fresh asparagus, chocolate mousse, currant cake, dainty cookies. Nofziger likes those.

But who sits where is often more tantalizing than the food.

Buchwald is always in the middle of the room. "You know he likes to be seen," says Georges Torchio, the maitre d'. Kissinger and Brzezinski wanted a quiet corner. Mel Elfin of Newsweek wants table 9. Columnist Robert Novak likes the slightly raised balcony. Hardly anybody wants the lounge. No scene.

The staff insists that Republicans, Democrats and other political beasts are treated exactly alike. Still, there is some evidence that certain Republicans are less equal than others. Former attorney general John Mitchell, for instance, wound up one day in the lounge.

"How did it happen?" says Anne Hartley sweetly. "He didn't have a reservation." Class Reunion

Former White House press secretary Jody Powell was a Class Reunion regular. Once Jimmy Carter called him there. The next day he asked "Whose reunion was it, anyway?"

These Friday nights, Reaganites swarm the bar. Unlike Maison Blanche, it's dark, cramped, decorated in a mishmash of college memorabilia and old movie posters. Ronald Reagan and Nancy Davis hang on a wall toward the front, embracing tenderly in a still from "Hellcats in the Navy."

But the real sign that "The Class" is going to weather the change in administrations came on Friday, March 20. On that night, Jody Powell was walking out the door just as Jim Brady, the current White House press secretary now hospitalized after a gunshot wound, was on his way in.

They decided drinks were in order. Immediately, Powell, behaving like a defeated gentleman, headed toward the Republican end of the bar. Brady, upping him one on noble behavior, gestured toward the back corner where the Carter staffers always sat. "No," he said graciously to Powell, "let's go to your section."

Thereupon they had four beers. Brady later said the talk was "Sympatico," a "good fly-on-the-wall conversation."

The Class Reunion's survival is hardly surprising, given that it was born as a Republican bar. Back in 1970, four staffers from the Nixon White House were returning from a long, long lunch at the Sans Souci.

"We decided we would walk around the block to get some air," recalls Ron Walker, who was special assistant to the president. "We walked past this place, and decided to pop in." The owner at the time, Jack Smigel, had just opened the bar after leaving the CIA.

"And I swear to God," continues Walker, "we sat here for the rest of the day and told war stories. From that moment forward, it became a Republican hangout." A short time after, the lines formed: Republicans at the front end of the bar, Democrats to the back, lobbyists in the middle, reporters near the phone.

The place on H Street, just two blocks from the White House, was especially popular during Watergate. As assorted administration types were disgraced and left town, they wept horror stories about fallen comrades into their beers. Afterward, the Nixon people told the Ford people about it, and then the Ford people told the Carters.

And now, the Republicans are back. It's like they never left. The place still looks like something from the '50s, and the tapes are Frank Sinatra. Behind the bar is a younger, smooth-faced Ronald Reagan is an old cigarette ad. ("My cigarette is the mild cigarette . . . that's why Chesterfield is my favorite.")

It went up Jan. 20. But the picture of Jimmy Carter, from his Navy days, stayed.

"It's been terrific," says Joan Grbach, the waitress-turned-manager who won't say whom she voted for. "After the Reagan people won, the Carter people were saying, 'Oh, God, what are you going to do with all those Republicans? And I thought, 'Well, you know, it's good for business. . .'"

Indeed it is. Grbach ran out of house vodka during inaugural week, and every Friday the place is jammed with staffers from the various White House offices. It's generally not the Meese, Baker and Deaver crowd (they go home to children and wives), but instead, the younger assistants and deputies who aren't household names.

Among them is Rick Ahearn, a White House advance man. He wears a three-piece suit when he drinks, and also recoils at the thought of doing anything as uncivilized as Hamilton Jordan allegedly did that night at Sarsfield's.

"We don't have such episodes at the Reagan White House," he announces. "I certainly have never thrown a drink on anyone in my life."

Clearly, this is not the Sarsfield's crowd that dressed in jeans and said, as political consultant Terry O'Connell did in 1977: "You go there because you can sing or dance or jump on the bar or pour ketchup on chairs or drop trou. . ." At "The Class" these days, they're wearing basic Republican: dark suits, white shirts, pleated skirts and pearls.

"Carter staffed his administration with a lot of people who were young, who'd never been in politics before," says Grbach. "But these people are older, more sophisticated."

"They're a little less jovial," says the bartender, Jeff Fellows. "I think it's part of the newness -- they're watching their Ps and Qs. But generally, it's a more staid group."

So what's it going to take to loosen them up?

"More vodka," he says.