The most talked-about no-show at last night's International Horse Show dinner and fancy dance was "The Black Stallion".

It seems that Cass Ole', hero of the "Stallion" movie, was stuck in a broken-down horse truck between here and South Carolina.

In any case, the famous horse will be here by Monday to go to the White House for a benefit for the National Center for Therapeutic Riding, one of Nancy Reagan's favorite charities.

It's just as well that the stallion didn't make the dance last night.

Last year, he slipped on the dance floor. Right in the middle of all that shimmering satin and silk. And then relieved himself on the carpet a little while later.

This year, bejeweled equestrians paid $500 a ticket to saunter through a jungle of rubber tree plants, technicolor orchids and every other shrub imaginable at the Botanic Gardens. About $70,000 was raised from the 150 who attended.

Among those attending the annual event were co-chairwomen Suzanne Block, wife of the secretary of agriculture, and Marilyn Lewis, wife of the secretary of transportation. Secretary of Commerce Malcolm Baldrige was there, as was Wyatt Stewart, finance director of the Republican Congressional Committee, and True Davis, the former ambassador to Switzerland.

The pre-dinner cocktail situation was rather interesting. Three full-size bars were obscured behind a virtual forest. Nobody ever saw them. A half-dozen waiters in snow white shirts stood with trays of drinks. It was a little bit like horse-trading.

"Hey, you got a scotch and water over there," called one waiter, obviously panicked.

"No, but I got a scotch and soda," yelled back his coworker. "Or do you want a bourbon and water?"

"Where's my champagne?" whined one woman, a guest.

"This is the perfect function to be showing Krug champagne," said Knight Fee, president of Premie're Wine Merchants, which donated a case of champagne as a door prize. Fifty dollars a bottle; $600 a case. "People in a horse group are definitely the kind who can afford to purchase Krug champagne."

After all, it is the champagne of the queen.