Joseph Papp came to the Kennedy Center yesterday and promptly threw two curve balls at the 1,200 area high-school and college students who had come to participate in an event called The Annual Seminar on Theatre.

His first mistake was failing to be Cloris Leachman.

"A lot of these kids just came to see her," said Jim Mumford, chairman of the English department at Archbishop Carroll High School in Northeast Washington.

"You know what it is?" asked Neil Stern, theatrically inclined student at Washington-Lee High School in Arlington. "It's a trick. They say they're going to have a celebrity, and they don't."

Leachman had agreed to participate but cancelled out.

The second thing that took some of Papp's listeners aback was his strongly worded assault on the value of academic theater training -- delivered while the seminar's chief organizer, C. Wayne Rudisill, who happens to run a theater school, sat impassively next to Papp on the stage of the Kennedy Center Concert Hall.

"Academics and theater do not particularly mix well," said Papp, who is the founder and producer of the New York Shakespeare Festival.Earlier, he had told a group ot students from the Theatre School, a two-year professional school in downtown Washington, that "whenever I go into a drama school, my hackles go up. An academic structure is death. . . .

It's a waste of time."

Peter Chewning, a first-semester student at the Theatre School, said he agreed with Papp. "You've got to get in there and do it," he said.

But Chewning, who hopes to be a writer/producer/director, expressed what seemed to be a majority sentiment that yesterday's seminar had been entertaining and worthwhile. The students, many of them accompanied by their English and drama treachers, had each paid $2 for the day, which included a choice of workshops on subjects from improviazation to costume design to stage management.

Bob Kelly, a major Broadway makeup man and wig maker, demonstrated his techniques in the AFI Theater, turning a young black woman into an ancient-looking bearded Asian mystic. For an encore, Kelly gave a second volunteer a massive bleeding sore on the black of her hand -- with a few dabs of latex, pencil and red paint.

Upstairs in the Atrium, meanwhile, 600 musical comedy aspirants were stepping to the music of 'There's No Business Like Show Business."

One reluctant dancer later described himself as "about as graceful as a Mack Truck." But Papp would have none of it. "When your spirit is straight," he said, "you'll walk straight. People are not naturally clumsy.

"Everyone who goes into the theater must be somewhat romantic, a little foolish," said Papp in his speech. But he warned his listeners of the high risk of failure. "If you have your eye on Hollywood, being a big star in movies and TV, I suggest you forget it. The thing is to try and find a place where you can work at your craft with people you respect."

Papp was also in Washington to look for funds to bring the Moscow Art Theatre here next spring -- a plan that is jeopardy -- and to talk to Kennedy Center chairman Roger L. Stevens about future joint productions.