The National Gallery of Art tossed what some art lovers decided was its first costume party in history under the guise of a luau last night, and it took several mai-tais or Tonga punches for a few in the crowd of 250 to adjust.

Nobody, for instance, would have expected to see the venerable Paul Mellon, Mr. NGA himself, show up at a pig roast, much less wear a floral lei over his impeccably-cut Saville Row pinstripe.

Neither would anyone have expected to see NGA Director J. Carter Brown in an aloha shirt, his naked toes peeking out from leather sandals for all the world to see. ("Don't say they're Greek sandals," pleaded his wife, wanting to keep the focus of the evening on culture of the Pacific Islands.)

And certainly the last thing anyone would have dreamed was that multi-millionaire art collector Armand Hammer would crash the party, especially after an all-night flight from the West Coast and a day of testifying on shale-oil development before a U.S. Senate committee.

Yet that's the kind of party it was on a warm summer's night arranged by Brown's NGA staff, with an assist from the Hawaii State Society, as a preview of "The Art of the Pacific Islands" exhibition opening July 1. The show brings together in the East Building more than 400 art objects from Polynesia, Micronesia, Melanesia and New Guinea and is said to be the most comprehensive of its kind ever assembled.

The day began around 6 a.m. on a south lawn by the Gallery when retired Navy commander Martin Dana and John Lopes, a past president of the Hawaii Society, started digging a pit 7-by-4-by-3-feet deep.

After one false start (they hit a pipe) and one sizable boulder (which they dated and inscribed to NGA's Carol Fox) they planted their wood, lighted it and waited for five hours before burying two 100-pound pigs which would bake, smothered by banana leaves stuffed with hot volcanic rocks and covered with earth for upwards of eight hours. When somebody tooted on a conch shell last night, it signalled that the pigs were ready. "High chief" Brown and visiting "high chief" Leo Falcam, governor of the Micronesian state of Ponape (and one of three such governors present), were served the first pieces.

"They smile," said Mahina Bailey, who chanted the blessing, "and you can begin the feast."

It began a half hour later, however, as Gallery officials delayed the start of dinner while awaiting Paul and Bunny Mellon's arrival.

Inside the Gallery, guests were seated at long tables of 10 to be served everything from salted salmon with tomatoes and scallions (kamano lomi), baked pig (kalua pua'a), beef, port and spinach in ti leaves (lau lau); cooked chicken with rice (moa laiki loloa to coconut cream dessert (haupia).

Standing guard over the exhibit, on the floor below, was the 79-inch tall, 1,000-pound Hawaiian war god Kukailimoku, on loan from the Peabody Museum at Salem, Mass. It was the first time the figure has left the museum since arriving there in 1846. It was carried outdoors when the museum caught fire in the 1870s, according to Carter Brown.

"The curator rushed in and carried Kukailimoku out of the building himself. The next day it took seven men to bring it back inside, which just shows you how the adrenalin can flow." CAPTION: Pictures 1 and 2, From left: Mr. and Mrs. Paul Mellon, Mrs. J. Carter Brown, J. Carter Brown and Mahina Bailey; Photos by Harry Naltchayan - The Washington Post