You can't fault Steward Mott for throwing a dull party.

Last year, with the advent of his middle age (he was newly 39) the General Motors heir gave a medieval feast in a New York City cathedral, dubbing himself "the Earl of Mott," donning purple velvet andermine, and greeting his guests with a speech in Chaucer's English.

This week, as more traditional New Yorkers went to the primary night parties of the politicians of their choice, Mott announced that "politics - especially New York City politics - are a circus." And he invited 1,000 friends to spend primary evening at a real circus: the tiny "Big Apple Circus" in lower Manhattan's Battery Park.

It was, on many levels, a satisfying arrangement.

Philanthropist Mott, the champion of liberal causes and liberal politicians, estimates he gives away a half-million dollars a year. And the Big Apple Circus, a cozy, one-ring outfit which prides itself on the "intimacy" of its show and features a "killer mole" act, is currently losing $8,000 a week and can certainly use Mott's money.

Also, while Mott this past political season gave fund-raising events for six of the seven Democratic mayoral candidates, as of his primary night party he had to confess he still had no favorite - and that having a benefit for a circus on primary night seemed a convenient way for him and his friends to avoid having to attend any one political celebration.

"To me the whole race was just so much more confusing than clarifying, I just couldn't decide. I wouldn't have felt comfortable celetrating with one special politician," said Mott Thursday nigth. "And it was the sort of race where one wondered why towards the end Badillo and Sutton and Harnett stayed in . . ."

Normally more than candid, Mott refused to say who had finally gotten his vote.

"Let's just say I got it down to two of the top four," he said.

And then?

"I flipped a coin," he said.

On the subject of his new philanthropy, the non-profit New York School for Circus Art and its Big Apple Circus which opened here this summer as New York's first resident circuit, Mott was more direct.

"I dont' usually give my money to circuses," siad Mott, whose past causes have included abortion reform, the Equal Rights Amendment, and Ralph Nader, "but I saw this circus in August and I loved it. It's in the traditional of the European one-ring circus. It has a simple linear quality; it's not like being at Ringling Brothers, which is like watching Hamlet in one ring, Romeo and Juliet in another, and God knows what in the third."

He said this cheerfully enouth as, wearing a hip-length Big Apple Circus T-shirt, white trousers, and bright plaid sports jacket with both a pink rose and a yellow carnation in his lapel (Mott is rarely without a fresh flower), he greeted his guests Thursday evening, outdoors in Battery Park.

To Mott's right was a view of the Statue of Liberty and New York harbor. The little green circus tent and a yellow tent set up to serve hot dogs, beer, and apple juice was behind him, and an impressive view of the World Trade Center was to Mott's left. Nearly as impressive as the veiw, however, was the Mott stood at the circus gate for an hour and a half greeting nearly all of his 1,000 guests by name, asking them about their recent trips abroad, making small talk about their causes. (I get 10 pieces of mail from you guys a week," Mott told Mike Beard, the director of the committee for the control of handguns.)

The guests, who Mott aides reported had been selected from the 4,000 names on Mott's three Rolodexes, included actress Lauren Bacall and writer Kurt Vonnegut, artist Robert Grossman, Washington friends Steve Martindale and Jack Quinn and Mott's long-time pal, John Hunting, of the Dyer-Ives Foundation of Grand Rapids. ("Stewart and I got into the foundation business about the same time, 10 years ago," said Hunting.) Keith Stroup, director of the National Organization for the Reform of Marijuana Laws, a $15,000-a-year Mott cause, attended the party with a marijuana leaf pin in his lapel. ("No it's not real gold, it's just something we sell for a dollar and a half to make money," he said.)

After a poem of greeting by Mott in the center ring - and a brief talk in which Mott cheerfully said that the apple juice served that evening was Red Cheek brand rather than Mott's because his family had declined to contribute and that was fine with him because Red Cheek was better than apple juice anyway - the guests, and their children, gave their full attention to the circus.

As heralded, it was a small-scale affair, New York City on a homey level.

Housed in a small tent, with bleachers that ran only eight tiers deep, the show was part professional but largely circus apprentices and amateurs. It included a "big lady" clown and a teen-age tumbling group. "The Back Street Flyers," all of whom were Harlem hight school boys who had been studying at the circus school for only six months. The orchestra numbered five, the circus animals - not counting the invisible "Killer Mole" - numbered two.

But at the end of the show the elegant crowd applauded the little circus wildly. And the show's directors, who blame the circus' out-of-the-way location for its current financial problems, in return appreciated the appreciation.

"The difference between us and a big circus, which some people don't understand, is that here you can see a performer's face, see how he looks when he makes a miss, but also see the joy; see his face when he comes off a double back flip," said Paul Binder, 33, the professional juggler who founded the show. "Here when a trapeze artist flies, we all fly. When a clown falls, we all fall. . .you know one of our flyers, it was only her second time performing tonight, and she was so nervous and we were all nervous with her. The first time she performed was only last Sunday and we were all so excited we cried."

he added his own assessment of Stewart Mott's primary night party.

"It's terrific, it's a bigger audience than we've ever had," said the man from the real circus. "Maybe some of these people can keep us going."