It was Young Republican Demonstration Time at Constitution Hall last night. There were some young Democrats too, but they were disguised as Beach Boys fans for the Inaugural Youth Concert.

Anthony Rogers, 18, looked atypical -- his well-worn jeans, University of Kentucky jersey and black leather jacket stood out in a sea of good Republican cloth coats. "I'll be dressing up tomorrow," he confided in a Kentucky cadence. "We were kind of hoping for a loser crowd tonight, added his best friend, Craig Eastham, lead singer for Broken Glass, a Southern rock 'n' roll band out of Somerset. Rogers may move to Washington next year; Daddy is newly elected member of the House of Representatives, Harold Rogers (R-Ky.).

Before the concert, most of the crowd milling in the lobby professed their Republican roots rather than Beach Boys fandom. "I don't even like the Beach Boys," said one recipient of a free ticket. "But the price was right." Bob Wasko, a student at a mortuary school in Pittsburgh, also got a free ticket and offered a discount on a burial if his name got in the paper.

Three winsome Republican belles got their tickets with a wee bit of artifice. Sherrie Sandy, who does public relations for the Georgetown Business Association, hung close to pals Kim Timmons, an Inaugural Committee volunteer from Denison College in Ohio, and Marshall Persinger, a student at the University of Virginia.

Working from a set of facts and implications, Persinger told the ticket committee that "our roommate [Margaret Molster] was going to marry Marvin Bush [the vice president's son and a recent UVa. grad] and our tickets should be here somewhere . . . the connection was honest," she said disarmingly.

Police dispatcher Greg York, 27, from Butler, Mo., wandered around in a full-dress tuxedo and a Cole Porter expression. He was the only penquin in the house. "I misread the book," he admitted. "But it's better to be overdressed than underdressed." Greg York was ready for tonight's Youth Ball.

The Beach Boys came on, finally, and the cheers were as ecstatic as if the house had been papered with fans. People had also cheered the warmup comedian during his impersonation of the dollar from 1945 to 1980. They even cheered the thought of a Richard Nixon comeback. But the cheers were loudest and constant from the opening bars of "California Girls," which the Beach Boys wished they all could be. The Young Voters Committee hummed their own inner lyrics: "Wish they all could be . . . registered Republicans."