It was wall-to-wall fur coats last night on the mezzanine floor of the National Theatre.

It was a party to celebrate the opening of "The Kingfisher," and also to celebrate the National Theatre's 144th birthday -- although the National Theatre organization manages to make just about every party it throws into some type of commemorative celebration. ("We can't let people forget that the wrecking ball was almost here," said one National supporter.)

Against all odds, almost 200 people managed to maneuver past each other, past the vegetable table and the table with bowls of melon balls to dip in melted chocolate, and past harpist Stella Gliechmann, who injected the one element of calm into the evening with notes of Debussy.

"At least you can move a little -- if you go to the Russians' you can't move at all," said one good-natured veteran of Russian embassy socials.

Those who were both lucky and agile got close enough to talk to Claudette Colbert and Rex Harrison when they swept through the party. The other actor in the play, George Rose, was reportedly seen somewhere downstairs in the lobby. "I think the crowds scared him off," said one guest. d

HUD Secretary Moon Landrieu was not fortunate enough to see the stars everyone was raving about. "We were just happy to be part of all this."

Alexis Smith, naturally, had a little more access. She also had the night off because the Warner Theatre, where her own show, "The Best Llittle Whorehouse in Texas," is playing, is dark on Monday nights. Swathed in a white fur jacket and accompanied by her husband, actor Craig Stevens, Smith stood in the office adjacent to the main party, and was greeted by other guests. When Colbert, in black mink and black sequins, was ushered in, Smith clasped her hand.

"Claudette," she said, and Colbert paused, her smile never flickering.

"Alexis," Smith added quickly.

"Oh, God" Colbert cried, her smile broadening. "You're here!"

"It's delicious," Smith said earlier of the play. "All three of them are a joy to watch."

Colbert moved easily through the room, graciously accepting people's personal rave reviews of the show, declining with her hand a proffered glass of champagne. When greeted by the French ambassador to the United States, Francois de Laboulaye, and his wife, Colbert spoke to them in animated French, much to the ambassador's delight.

"We really had fun tonight," said Colbert. "We could really feel something there with the audience."

"Do you still play poker?" asked Martha Clarke, who works for the American Cancer Society. A friend had told Clarke that Colbert played regularly with a group of friends.

Colbert's eyes widened in amusement. "Me? You must be thinking of Constance Bennett. One night we had a party -- Constance Bennett, David Selznick, they were all there playing in the living room. I finally went to bed. The next morning, my husband, who was a surgeon, got up at 5:30 in the morning to go to work and they were still playing."

Colbert, who plans to return to her Barbados home after the run of this play, pulled her coat around her after 15 minutes of partying, ready to leave. But then a voice piped up: "May I introduce you to the ambassador or Surinam . . ." Colbert smiled, accepted the introduction, and cheerfully trooped on to a few more.

Rex Harrison appeared later for an equally brief period, noting that he had made his American stage debut at the National -- in "Sweet Aloes" in 1936.

"I think he's sexy," said guest Evelyn McCoy.

Later, after Colbert and Harrison had left, Alexis Smith cut a birthday cake for the National Theater, and local actor and Prince Georges County security officer George Bossard led the crowd in a chorus of "Happy Birthday."

"They say there should be more older people on TV," observed Frances Humphrey Howard, sister of the late Hubert Humphrey and a member of the National board. "This play was done with such style and intimacy -- by two older people -- that maybe it will lead the way. After all, there are many of us late-middle-aged people, shall we say."