"If you have to spend two years of your life making a movie like 'Superman' just to meet the Kennedys, then it's worth it," said "Superman" producer Richard Donner last night as he stood elbow-to-elbow with Eunice Kennedy Shriver in the den of her Rockville home. "After all, they are our royalty, aren't they?"

Last night at the Shriver home, Timberlawn, Eunice and Sargent Shriver threw a black-tie dinner-dance for 350 guest who paid $500 to be there. And as one might expect from the Kennedys, it was a sparkling group -- movie stars mixing with politicians mixing with New York business executives.

The occasion was the kick-off dinner for Washington's weekend of Superman-it is -- two days of parties and other events culminating in the world premiere of the Warner Bros. film "Superman" at the Kennedy Center Sunday night.

Proceeds from the weekend will benefit the International Special Olympics, which was founded by Eunice Shriver, who is its current president. For those who shelled out $500 for the top-priced tickets, dinner at the Shrivers was included.

"I feel so out of place in these elegant surroundings," deadpanned Bill Paley Jr., son of William S. Paley, chairman of the board of CBS, who in his three-piece tuxedo was mistaken by one guest for a lawyer. (Paley is co-owner of Washington's Gandy Dancer restaurant.) "This reminds me of the first time I went to a rock concert wearing a suit. I saw all these kids in long hair and there I was all dressed up; then like now I was surprised but delighted."

Which was the reaction of most of the guests last night to the Shriver household. In the name of Sweet Charity, the place had been turned into a party playground. Greeted in the Shriver den resplendent with a gigantic Christmas tree, guests could wander through a tent-covered addition running the length of the house.

Later, guests paraded down an adjoining ramp to yet another massive blue-and-white-striped tent, featuring a dance floor and candle-lit tables for 10.

"Ooh, I'm on a high," squealed Maria Shriver, the Shrivers' 23-year-old daughter, just before the arrival of her boy friend, muscle man Arnold Schwarzenegger, whose arrival was greeted by an effusive kiss from Maria. Schwarzenegger, something of a superman himself, said he liked the comic book Superman because "I like bigger-than-life-size things." He went on to deny reports that he and Maria are living together. But love, well, that was something different. "I'm very heavy in love," assured Schwarzenegger with a glance toward Maria Shriver." On the 1-to-10 scale of love, I'm 10 in love."

However, another of the most recent Kennedy escorts, filmmaker Peter Davis, who has recently been linked in reports with Jacqueline Kennedy Onassis, was much more vague about his romantic intentions. Asked about Onassis, who was not at the party, Davis shyly replied, "I just wouldn't talk about my personal life and I certainly wouldn't talk about anybody else's. Is Jackie here? I don't believe she's here," he hedged. "Look, I just took the shuttle down with my kids."

Christopher Reeve, who plays the Man of Steel himself in the movie, seemed positively delighted with the whole shebang. "I can't believe it, I just want to shake your hand," he said as he ran up to meet Joseph Shuster, one of the creators of the original Superman comic character.

Reeve arrived with his girlfriend, British model's agent Gae Exton, who Reeve said he met when he stopped on her toe in a lunch line while making a film in England. For her part, Exton appeared slightly bemused by all the fuss surrounding Reeve.

When one observer asked how it felt to be the lady in the life of one of America's burgeoning sex symbols, Exton laughed, "I never thought of him that way. I can't see that all this will change him at all. Hopefully. But those could be famous last words."

Before Reeve could respond to that, however, he was pulled away to join Sen. Ted Kennedy for one of the endless shots of the two demanded by the crowd of photographers and cameramen.

At one point, the senator mused about what Superman had meant to his life. "I think Superman represents for all Americans a sense of hope in being able to overcome extraordinary challenges... which is why his association with the Special Olympics is so appropriate. The retarded and handicapped have much to overcome as well."