King and queen for a day -- or at least until the tide rolls in. Mr. Blandings builds his dream house -- then watches the waves tear into the turrets and leave lumps of sand where the drawbridge used to be. As many rooms as you need, ocean vu, low maintenance, this one won't last long.

Not even the flightest of the three little pigs would have built his house of sand, but thousands of unflightly people brave blisters and backstrain to bucket brigade Taj Mahals, Mont St. Michels, even fatter-than-life beach-sitters into ephemeral existence.

Sand sculpture used to be the domain of kids with pails and shovels, but now it's an art form and adults get to play, too. The serious architectural statement -- the Windsor Castles, the whale-size whales and the 12-mile-long Camelots -- are usually made in California; but this Saturday, Rehoboth Beach hosts its annual sandsculpture contest, and anybody can go turn a piece of beach into a castle or a whale.

"A castle because it's classic, and a whale because we sponsor the contest," said Dennis Forney, editor of The Whale. (It's a great journalistic tradition: Le Figaro has sponsored a similar event at La Baule on the Normandy coast for 25 summers.) Rehoboth's competition is friendly but keen.

"We really got into it by accident," said Bette Doney, matriarch of an artistic clan that has copped prizes for the past two years in a row -- in 1978 for a Jonah and the Whale, with Jonah's feet kicking from the whale's mouth, and in 1979 for a group of fat bathers, entitled "Beached Whales."

To avoid imitators, she declined to reveal the subject of this year's family effort. It was, she said, chosen from among several ideas by a vote of all nine family members, including two sons-in-law. In addition to shovels and buckets, the Doneys bring lots of old newspapers to the beach.

Wet newspapers keep the sculpture moist," advised Bette Doney. "They don't do the judging until quite late, and if the sculptures dry out they fall apart." Picking just the right spot for your work is crucial, too, she said:

"You don't want to be too far from the water, because the sand is too dry and you'll have a long way to haul water," she advised. "But you want it to be safe from the tide. You also have to work quite fast and keep wetting the sand. Bob, my husband, does the sketch and everybody is assigned a section. The thing that's going to pull it all together -- like the boat in the whale's mouth -- we leave untill last. That way it's a surprise and nobody steals your idea."

Norman Richard Kraus, the uncrowned king of sandcastle art, said that he would reveal the subject of his annual Labor Day castle-building extraganza if he knew it. "I'm still researching," the California architectural designer said on the phone. "I'm looking at Mayan structures, but I'm not sure that would work from a practical engineering standpoint." Mayan temples have been reproduced on benches. But not in anything like the scale Kraus has in mind: "We're thinking in the rang of 400 to 1,600 tons," he said. "We built our first megastructure -- our first tractor-assisted project -- in 1969. It was an experiment. We only used about 60 tons of sand and built a fantasy castle." Since then, Kraus and his team have reproduced the French walled city of Carcasonne, Windsor Castle, Mont St. Michel and Heidelberg Castle. Heidelberg, last year's effort, towered 22 feet above the bench and displaced 600 tons of sand; but bigness is not all, and Kraus is equally concerned about historical accuracy. "We built Heidelberg as it was in 1690, working from the original floor plans," said Kraus.

According to other research done by Kraus, serious sandcastle-building goes back to the 12th century, when German emperors built prototypes of proposed castles in sand along to Rhine to study them in terms of defense. Although Kraus and company usually plow the sand into a mound with a tractor, water it down with hydraulic pumps and pack it with the 30-ton tractor, he thinks the basic method -- the "compact-sculpt" method -- can be adapted to the needs of smaller-scale builders. "Pile the sand up in the shape of a volcano," he suggested. "Make a crater on top and keep pouring water and more sand into it. Keep it as vertical as you can. Jump on it and pound the sides until it's so dense and hard it can be carved easily."

But once you've solved the technical problems, you still have the pyschological issue: How do you deal with the fact that sun, wind, trampling feet and water are bound to destroy your masterpiece?

Firt off, you don't think of it as destruction but as "reintegration." "You're reshaping a portion of the environment," said Kraus, "and in many ways the reintegration is the most beautiful part."

The Doneys also take reintegration philosophically: "After the judging we take a lot of pictures," said Bette Doney. "Then, just so nobody else can trample on our sculpture, we trample on it ourselves. Next day we go down to the beach to see if there's anything left. Generally, there's just a shapeless mound."