Two bewigged, redcoated trumpeters blew tinny salutes as the most honorable guest puffed up the orchid-lined staircase of the Renwick Gallery. Upon reaching the summit and the gallery's Grand Salon, they were forthwith swept into the dizzying swirl of The Waltz.

The Waltz. That was the theme for the soiree thrown Friday evening by the Smithsonian Institution for its most generous contributors. And judging from the hedging toes, colliding shoulders and mumbled pardons, Washington society seems to have had its waltz steps in mothballs for a while.

As repeated strains of "Tales of the Vienna Woods" continued to impede conversation, The Waltz looked as if it were getting easier. Men took on wistful, faraway looks, their lady partners relaxed. Husbands danced with their wives, and then led them out into the anterooms to drink champagne and eat strawberry pastries encased in red gelatin.

White House social secretary Muffie Brandon did The Waltz with her husband, Henry, chief correspondent for the London Sunday Times. A former consultant whose duties included locating corporate funds for museum projects, Muffie Brandon rationalizedabout the Reagan administration's proposed 50 percent cut in the federal arts endowment as she repaired to the dance floor sidelines.

"The arts will flourish despite any cuts," she said with a conforting smile.

"It won't be easy, but the arts will flourish on their own. You can't stop the arts."

The lone senator in attendance, Claiborne Pell (D-R.I.), was more out-spoken about the cuts in question.

"I'm deeply disturbed," said Pell. "I think they are excessive, and I trust the size of the cuts will be reduced."

British Ambassador and Lady Henderson hosted the highbrow affair, filling in for Smithsonian Secretary S. Dillon Ripley, who was off on a "research" mission to Sri Lanka. Seated at a front-row table whose occupants full decoration regalia lent a very British air to the surroundings, the ambassador predicted that when his country's prime minister, Margaret Thatcher, makes her pilgrimage to the White House later this month, she and Ronald Reagan will get along splendidly.

"They'll certainly exchange views about their policies," Henderson said.

Loosening up a bit, the band played "New York, New York" between waltzes. Smithsonian regent David C. Acheson discussed how many miles high you'd have to pile up $1,000 bills before you had a trillion dollars. Meanwhile, about that many miles of taffeta swished throughout the Renwick, for it was clearly a taffeta night -- purple taffeta plunging low, black taffeta gathered in a bustle, pink raffeta ruffled straight up over the neck.

It was just past midnight when, suddenly, the band abandoned The Waltz and led a full-fledged assault on The Charleston. Heretofore sedate steps became kicks and spins. Lady Henderson's gray, netted skirt flew up over her heels, and her husband's tails spun. Another woman twirled chiffon in hand like a flapper would a string of beads. An elderly gentleman cut rug relentlessly, changing partners midstream. Across the room, the strap on a backless dress gave way under duress, requiring its wearer's partner to hold the pieces together and lead his lady off the floor.

Then, it was over as quickly as it had begun. A breathless flapper walked to her table.

"That beats the waltz, doesn't it?" she said, wiping her brow.

It was hard act to follow, and many waltzers began their descent down the marble stairs and into the rain. On their way out, the ladies got Godivas to munch on.