I. M. Pei, the architect, was not just a little pleased that his casual odyssey last summer had netted such willing Greeks bearing gifts.

"The essence of art history is all here," he said, grinning broadly. "When I saw it at the Benaki Museum (in Athens) I said we simply must have it at the National Gallery. She said she'd love to send it but would have to ask the Greek government."

She did, the Greek government said yes (under a 2-year-old law permitting antiquities to leave the country on loan) and last night Dolly Goulandris, her shipping magnate husband Nico and 166 pieces from their priceless collection of Cycladic art were comfortably ensconced in the Pei-designed East Building for a gala black-tie dinner and exhibition preview.

"This is a great, great pleasure," said Goulandris who had bought a sea-blue crepe Guy Laroche original for the occasion, "thanks to you."

Apparently thanks to a number of people, including the National Gallery's globe-trotting director J. Carter Brown, who flew to Greece last autumn to nail down the deal after Pei returned home saying the Goulandris collection would go "pefectly" in his building.

By February, special packing crates had been designed, with each object fitted into its own Styrofoam-filled "nest," according to Christos Doumos, director of antiquities in the Greek Ministry of Antiquities.

"Even if a case fell in the water, it would float," according to Doumos.

The cases were put to rigid tests, he said. Some were dropped four floors (contents emerged unharmed), others set fire with temperatures rising to 1,500 degrees centigrades (inside the temperature registered normal).

Guests numbered more than 100 and hailed from Greece (10 members of the Goulandris family alone were there), from New York, Minnesota (they are Mayo Clinic regulars) and from throughout the nation's museum community.

"There is so much competition for blockbuster exhibits that people in the United States have their tongues hanging out," said Lee Kimche, director of the Institute of Museum Services at Health, Education and Welfare. "People don't get this kind of experience from watching television or reading newspapers."

Dinner was intentionally cold ("Most people aren't that secure," marveled New Yorker Jerry Zipkin of Pamela and Carter Brown's menu choices) and featured "veal Styros" (What does it means, 'Styros'?" asked Doda Goulandris Voridis of Athens).

It was announced last night that the Greeks are getting a temporary gift from Washington as well. Leaving the National Gallery in June to help celebrate the anniversary of the Benaki is El Greco's "Laocoon."

"It holds a speciial meaning to our country," said Dolly Gaulandris, in making the announcement. "The gesture is greatly appreciated." CAPTION: Picture, Ambassador and Mrs. Menelas Alexandrakis, left, greet Dolly Goulandris; by Harry Naltchayan - The Washington Post