The Republican aristocracy took over Washington this weekend, making it safe again to put on diamonds, designer gowns and -- speaking generally -- the dog.

Even political talk, normally the staff of life at most Washington parties, was momentarily passe Saturday night. At the C. Wyatt Dickersons' dinner-dance in McLean, everybody played down Iran and the hostages even though the latest developments toward their release were being relayed into the walnut-paneled library directly from the State Department for the benefit of one guest -- the president-elect.

As one veteran partygoer put it later: "We were all on our best behavior. We knew the Californians were just here to have a good time and that they don't yet understand what makes this town click."

Most seemed to know what makes a party tick, though, and the women came prepared in their full-length minks and sables over their St. Laurents, Oscar de la Rentas, Halstons, and Bill Blasses in much the same way they might at a Hollywood opening.Instead of searchlights overhead Saturday night, however, there was a helicopter scouting the way for a motorcade (an ambulance brought up the rear) that deposited Ronald and Nancy Reagan at the Dickersons' front door shortly after 8:15.

Sporting the ruddy color that television makeup artists strive on, Reagan alighted from his limousine with a "no comment" to a question about whether he thought his appointment Tuesday on the steps of the Capitol might be hastening the release of the hostages.

"I'm just going to wait with my fingers crossed," he said, hanging back for an instant while Nancy Reagan, wearing a black-sequined Adolfo and clutching a black fox boa around her one bare shoulder, darted for the door.

Trying to sneak in the back way while reporters and photographers huddled in the freezing cold at the front door were Frank and Barbara Sinatra. Even when they spotted him he never changed his pace; neither did he offer any comment on rumors that had Reagan naming him U.S. ambassador to Italy.

The guests of honor were a Los Angeles industrialist and his wife, Armand and Harriet Deutsch, whose friendship with the Dickersons goes back to an introduction years ago by Phyllis Cerf Wagner. The Deutsches, says Nancy Dickerson, introduced her to Irving "Swifty" Lazar, the Hollywood literary agent, who persuaded her to write a book about her experiences in Washington as a televison correspondent. A paperback copy of "Among Those Present" is kept in the Dickersons' pool house for bathers who haven't read it.

The Deutsches' friends and those of the Dickersons added up to more than even Merrywood, the spacious mid-18th-century-style mansion that was Jacqueline Kennedy's girlhood home, could accomodate at one sitting. So the Dickersons decided upon Pisces, a private club in Georgetown, for a satellite party, with the job of hostess-in-residence filling to Tish Baldridge, the Kennedys' social secretary at the White House who is currently advising Nancy Reagan.

It opened the way for the inevitable status jokes about "A" and "B" lists, but Nancy Dickerson solved it quite simply. She put out-of-towners, who included Reagan's intimates -- "kitchen cabinet" advisers as well as CBS anchorman Walter Cronkite, fashion designer Bill Blass, John Murchison's widow, Lupe, former ambassador Walter Annenberg and his wife, lee, cosmetics mogul Estee Lauder and husband Joseph -- at Merrywood. And she assigned in-towners -- such people as Illinois Sen. Charles Percy and Oregon Sen. and Mrs. Mark Hatfield, Inaugural co-chairman Robert K. Gray, former ambassador Elliot and Anne Richardson, Walter and Marie Ridder and President Carter's campaign director Robert Strauss and his wife, Helen -- to Pisces, the club Dickerson co-founded and now serves as both president and landlord. There were some in-towners among the out-of-towners -- financier Joe Allbritton and wife Barbara, Redskins co-owner Edward Bennett Williams and wife Agnes, and the British and French ambassadors, for example -- and some out-of-towners among the in-towners -- Continental Airlines president Robert Six and his wife, Audrey Meadows, and former ambassador to Denmark Guildford Dudley and wife Jane -- but nobody seemed able to figure out why.

So it was that the Dickersons seated 48 at round tables covered with white cloths centered with arrangements of apricot-colored tulip chosen to match the dress of a child in one of the Dickersons' collection of primitive children's portraits. The menu was identical to that served at Pisces and included the Reagans' most ballyhooed favorites: veal (this time prepared in chablis sauce) and strawberries (this time marinated in kirsch). While white-gloved waiters kept glasses filled with two French wines (a white Chateauneuf-de-Pape and a red Medoc) and a California blanc du blanc, attendants were hiding the entrance hall furniture upstairs and rolling up the Oriental rugs for dancing.

There were toasts, including one by Ronald Reagan on friendship ("He was in favor of it," reported Deputy Press Secretary Karna Small) and one by the hostess, who later threw protocol to the wind and asked the president-elect to dance. Appropriately, since the other Nancy ("A very 'in' name these days," reported Small) was dancing with the host, Howard Devron's band struck up "Nancy With the Laughing Face."

Frank Sinatra did not volunteer to sing it. While Barbara Sinatra, whose jacket was an explosion of sequined "fireworks," circulated among the guests, her husband continued the low-profile stance he adopted for the weekend. Friday night he skipped a party given by Chicago insurance tycoon W. Clement Stone and opted for a more intimate (and less publicized) dinner hosted by Madison Hotel owner Marshall Coyne.

There were souvenirs, at least for the Merrywood guests -- truncated lucite obelisks engraved with an excerpt from Reagan's pre-election-night speech. And like thousands of others coming to town for the festivities, millionaire real estate investor Jerry Zipkin, Nancy Reagan's special pal, brought along his camera.

The Reagans met everyone ("sometimes two and three times," said one guest) who managed to break through the snarl of limousines arriving from Pisces and departing from Merrywood. Inaugural co-chairman Charles Wick tried to calm his wife, Mary Jane, whose fury mounted the longer she waited in the cold for their car to take her home. Socialite Evangeline Bruce and Jan Cowles, were more tolorant of the delays. As they clutched their wraps around their shivering shoulders, their evening slippers tapped out quick cadences on the icy porch steps.

The Washington contingent, many of them getting their first close-up of the Reagans, listened politely as the Californians described the Reagans' friendly social style and their eagerness to get acquainted. One insider even confided that Nancy Reagan is already worried about White House isolation.

Reagan's "kitchen cabinet," at least, appeared ready to ease that problem with the same devotion they offered when they drew up a list of Cabinet candidates for Reagan. Some even talked of renting apartments in Washington.

"To be available when we're needed," was how one of them put it.