Mercea Cooley and Dwayne Brown didn't waste an instant. When Dance Theater of Harlem founder and director Arthur Mitchell invited audience members to show him D.C.'s latest dance steps, the teen-agers practically flew onto the Kennedy Center's Terrace Theater stage to strut through a number they called "The Southeast Walk."

"They're bending their knees in plie just like dancers do in classical ballet," Mitchell explained to the audience of nearly 500 cheering students who filled the auditorium last night for a lecture-demonstration that kicked off the company's Washington appearance.

Dance Theater of Harlem perform a week of similar arts-exposure programs for area students before beginning their week-long run in the Opera House beginning next Tuesday.

"Talent is only 50 percent of the ball game," Mitchell told the enthusiastic audience. "The rest is hard work.

"We advocate that everyone study dance because it's beautiful to see human beings really aware of their bodies."

For Cooley, Brown and about two dozen other members of the Southeast Tots to Teens Dance and Theater Group, the evening was their first at the Kennedy Center and their introduction to professional dance.

"I had no idea they'd be this good," said a wide-eyed Patreese Tyler, 12. "The way they move is sensational. They are really tripping me out."

Like many members of the youthful audience, Tyler had trouble keeping still as she watched the dancers twirl, jump and leap across the stage. k

"I know how hard those leaps are," noted 11-year-old Scharmel Giles. "When we do them in class, we've got to keep our legs 100 percent straight."

The greatest crowd-pleaser was a percussive number performed by male company members. "They are baadd," breathed Brown, 17, the oldest member of the Southeast Dance Group.

The group's director, Vendetta White, said, "I'm just as excited as the kids. I'm inspired to go back and work even harder."