Play the calliope! Watch Montgomery Meigs go up in fireworks! Tip back the champagne toasts! Swing wide the klieg lights! Turn on the fountain!

The National Building Museum opened last night in perhaps the most select of all the Pension Building's inaugural balls.

Some 200 guests, many of whom had been true believers for years in the great old 1880s building, came to a black-tie dinner amid general rejoicing and expressions of amazement that at last, the museum had opened. They shook hands with Director Bates Lowry and Robert Daniell, president of corporate sponsor United Technologies, beside the tallest Corinthian columns in the world.

As Wolf Von Eckardt, whose study won congressional support for the building, put it, "We are all saying, 'We did it!" Von Eckardt said that he first became interested when Louise Mendelsohn, wife of the famous architect Erich, complained that she had all her husband's drawings and papers "and no one wanted them. No one wanted Louis Kahn's papers. Frederick Law Olmsted's papers are still rotting away except for the few the Library of Congress could take. I thought the 'Building Building' should be a repository of architecture papers, with information you could call up by computer."

Architect David Meeger bragged that as assistant secretary of housing and urban development, he put up $35,000 to pay for Von Eckardt's study.

"I'm so excited," said Phyllis Lambert, a museum trustee, who persuaded her family to hire Ludwig Mies van der Rohe to design the landmark Seagram Building in New York. Lambert, an architect, is now head of the Canadian Center for Architecture, opening two years hence.

The soft lighting, as at candle-lit parties given by house-proud hostesses who have seen better days, spread a veil of grace over the great hall. Even people who in the harsh light of the day questioned the colors of the cortile, the vast reach of the roofed court, had to admit, under the softening effect of the light (and perhaps the champagne), that they didn't look bad.

Preservationist (and museum trustee) Richard Howland said of the controversial colors (bronze columns, pale lime-green and beige pink walls), "They're not my choice." But even the colors had staunch defenders. George White, architect of the Capitol, said, "the colors are historically correct." And he went on to say of the building itself, "It's unique, nothing like it anywhere. The space is noble. The restoration is a fantastic achievement." He, however, declined to move in. "Once you're in the Capitol," he said, "you don't ever want to move out."

Alan Fern, director of the National Portrait Gallery, once in charge of drawings and photographs at the Library of Congress, a prime lender to the show, commended the installation of the important "Building a National Image," the architectural drawing show that opened with the museum. "They've done a careful job of environmental control to preserve the drawings. The overall impact is spendid." Lois Fern, an editor, said she didn't find the exhibit cabinets overpowering at all. "They give an intimate feeling."

After the she-crab bisque, the loin of veal, the orzo with walnuts, the radiccio salad, the fruit and pastry cornucopias with sabayon sauce, and the toasts to all who kept the faith, the guests went out to watch as, on Judiciary Square, a panorama of buildings in fireworks expressed the glory of the birth of the National Building Museum and the rebirth of the Pension Building.