Would Bernice Chrysler Garbisch and Edgar William Garbisch have enjoyed the last, lavish party at their estate of Pokety on the Eastern shore?

"I hope so," said John Marion, chairman of Sotheby Parke Bernet, yesterday at Pokety, near Cambridge, Md. "But I'm afraid they would have been mad about the tent stakes in their lawn."

The rare and important American furniture and Chinese export porecelain collected by the Garbisches took two books to catalogue. The auction conducted by Sotheby's will be Thursday through Sunday. The collection is expected to bring from $3 million to $5 million. The estate itself is up for sale with a $3 million price tag for its 480 acres and manor house.

Yesterday morning, some 400 collectors, socialites and top antique dealers boarded four buses at the British Embassy parking lot in Northwest Washington for a picnic at Pokety, given by Marion.

Even those who found 9 a.m. Sunday early were mollified by silver baskets, packed by Ridgewell's, full of miniature croissants, round doughnut balls (the holes from doughnuts?), fresh fruit, coffee and tea served by a black-suited steward.

Clement Conger, curator of the White House and head of the State Department's Americana collection, divided his time between inspecting the furniture and greeting those he thought might buy it for his collections.

Albert Sack, "the rare and important" New York dealer in Americana was off in the butler's pantry gossiping with William W. Stahl, Sotheby's Americanan expert. Sack sold many of the fine pieces to the Garbisches over the years. "It's a wonderful collection," he said, "and Sotheby's have done a masterpiece of presentation."

No one could deny it. As visitors came into the great hall, the house looked much as the Garbisches left it when they died within hours of each other on Dec. 14, 1979. Flowers filled the great Chinese export porecelain vases; there were no ropes or barriers inside.

On the walls appeared to hang the jewels of Pokety, the Garbisches' splendid collection of native American art. Actually, that wasn't so.

"I can't find the paintings listed in the catalogue," said one woman. "And I've seen one I must have, no matter what it costs."

"Too bad," said another. "The paintings have all gone to the National Gallery of Art and to other museums. These are just photographs of the paintings and their frames."

Stahl said he'd ordered the color photographs ("they were cheap, only about $200 cash") because the house looked so empty and bland without the famous collection. "I guess I'd better put up a sign saying these are photos and not for sale," he said.

Everything else was for sale. A Federal inlaid mahogany and satinwood tambour desk and bookcase, for instance, is expected to go for $30,000. A block and shell carved Cuban mahogany kneehole desk in the Chippendale style is expected to bring $150,000 to $200,000. Even the family's magazines, books, television sets and curtains will be sold.

The major pieces of porecelain and silver were displayed in glass cases in a tent on the lawn overlooking Lecompte Bay and the Choptank River.

Large round tables were set with tablecloths and wine, but some took their baskets over to a magnificent brick wall along the water. Maurice Tobin, whose wife, Joan is the head of Sotheby's Washington office, said, "What I'd really like to bid on are the three miles of brick wall here. You'll never see one like that again."

The exhibition is open to the public today through Thursday from 9 a.m. to 4 p.m.