A curator from the Boston Museum of Fine Arts stood in the atrium of the National Gallery's new Center for Advanced Studies in the Visual Arts and stared at the surrounding six stories which will eventually hold library stacks and staff offices. His verdict: "We could be in the middle of IBM International Headquarters."

"How about the Hyatt Regency?" offered another skeptic, one of few among the 150 scholars, curators, collectors and lenders - the "brains of the art world" - who assembled for lunch yesterday at the gallery. They were there to celebrate two inaugural exhibitions, "Giovanni Battista Piranesi: The Early Architectural Fantasies" and "Master Drawings and Watercolors: Selections From the National Gallery Collection and Promised Gifts."

New Orleans museum director John Bullard shot a glance at the soaring space. "I wonder who will be the first rejected Ph.D. candidate to jump off the 6th-floor balcony because his fellowship wasn't renewed," he mused.

Other professors, young and old, from Harvard, Yale and NYU, said nothing, no doubt dreaming of having an office up there to jump from at some future date.Some admitted to hoping to rise to the top of the current "short list" of candidates for he job of director of the Center, which opens in 1979.

"We're on a tight schedule," said gallery director Carter Brown, as he led the way to the fourth floor, where cannelloni was served on tables set with potted red geraniums. "You know, Piranesi is one of the few old masters you can still buy for under $1,000, confided David Tunick of New York, one of few print dealers present. "The trick is to find those works printed in his lifetime. Andrew Robison has taken a major step toward sorting out these works in his show." Print curator Robison beamed.

"This building fulfills a lifelong dream of mine," said fit-looking former National Gallery director John Walker, in for the opening from Surrey, England, where he has lived with his wife, Lady Margaret, since his retirement. "The best nine years of my life," he said of his retirement. "I'd forgotten how hard it is to run a museum, and I'm proud to have brough Carter Brown on board."

"I know there are among you - not all of you - some very distinguished people," gaffed National Gallery trustee Franklin Murphy, who recovered from good-humored boos to introduce the widow of Gallery donor Chester Dale, donor Lessing Rosenwald and architect I.M. Pie. All stood and beamed, though Pei, in an aside, admitted he would be glad when they took the tables out of his atrium so that people could see the building "as it was meant to be seen."

"If I take more than one pear, will it ruin everything?" asked Colin Eisler, the distinguished young NYU professor, as he helped himself of two poires pochees au gingembre.

To top it all off, the group was invited to descend to the mezzanine level and meet Rosalynn Carter, who was wearing green silk and killing two birds with one stone by shaking hands alternately with NATO wives, who had also been invited in to see the building. After demitasse and giant strawberries, the scholars wandered off to avail themselves of the precious opportunity to view the art in the last quiet moments before the new museum was engulfed by the populace at large.