The Spruce Goose may finally lay a golden egg -- but for private enterprise and not the U.S. taxpayer, who fed it more than chicken feed all those years industrialist Henry Kaiser and later Howard Hughes were hatching it as the be-all and end-all of America's World War II troop and cargo planes.

The giant flying boat became a Hughes obsession, though it was never again airborne after he took it on its brief maiden flight in 1947. Now it may finally earn its keep after years of pampering. Taxpayers spent $18 million to develop the plane and after the war Hughes spent another $60 million maintaining it. He kept a 30-member crew in constant readiness, though he seldom paid a visit. When he did, it wasn't unusual for him and a few friends to have a picnic beneath the plane's 320-foot wingspan.

The way Hughes poured money into his grounded plaything, you would have thought he was expecting the president of the United States at any minute. Now, seven years after Hughes' death, the president is coming, and for the Goose's new keepers, the Wrather Corp., Ronald Reagan's presence will be the kind of publicity that can't be bought.

The Goose, a new tourist attraction in the Long Beach harbor area that includes the Queen Mary, will get the golden walk-through by Reagan Thursday night at a gala Republican fundraiser. His good friends, Jack Wrather and Bonita Granville Wrather, invited him out for the ribbon-cutting a month ago but he couldn't make it at the time.

Vice President Bush has already stopped by, Jimmy Stewart and Cary Grant have paid visits, and with Reagan's presence this week the Goose may take off financially for the first time in 36 years.

The Wrather Corp., whose Midas touch extends from oil and gas holdings and managing hotels at Disneyland and aboard the Queen Mary to rights to Lassie and the Lone Ranger, has spent $15 million on the Goose since leasing it from The Aero Club of Southern California. That's a small, private, nonprofit club whose members, coincidentally, include Wrather and Richard Stevens, president of Wrather Development.

The Aero Club got into the act in the fall of 1980 when Hughes' Summa Corp. gave it title to the Goose after a running battle with aviation buffs opposing Summa's plans to cut the plane up and give it to museums around the country. Summa's choice of a recipient had to have the blessings of the Smithsonian Institution, which gave them gladly. Five years earlier, the General Services Administration transferred the Goose to the Smithsonian, which owned it for a legal instant before trading it to the Summa Corp. for $700,000 and the historic Hughes H-1 Racer, now on permanent display in the Gallery of Flight Technology.