The young people were seen and mostly not heard at yesterday's Leadership Brunch for Young Americans, one of the inaugural warm-up festivities, except to applaud vigorously and often for their elders.

First they stood up and cheered for President Reagan's official swearing-in at the White House, the audio piped into the ballroom at the Marriott Crystal Gateway in Crystal City. Then the 400-odd fledgling conservatives, culled from high schools and colleges around the country, clapped for such Republican gray-hairs as actor Hugh O'Brian (salt-and-pepper), Georgia Rep. Newt Gingrich (thick and silver) and New York politico Lew Lehrman (thinning with white highlights).

"Ronald Reagan is the leader of a movement, and that movement is growing -- that's the whole story with the young people," said Gingrich, a former college history professor, while the waiters passed out Gingrich's 19-book suggested reading list, including his own tome, "Window of Opportunity."

"A lot of uplifting pep talk," said 16-year-old Ted Mills, a student at Robinson High School in Fairfax, appraising the occasion.

Neesa Hart, 17, state treasurer of the Virginia TARS ("Teenage Republicans") and head of the 400-member TARS at Langley High School in McLean, tried to explain the Republicans' appeal for youth.

"It's because at the stage we are now, we really remember just two presidents -- Jimmy Carter and Ronald Reagan," she said. "With Jimmy Carter, we couldn't go on ski trips and buy designer jeans because our parents were strapped financially. But then Ronald Reagan came in, and after a while we got those things."