On the eve of the Super Bowl, John Riggins was once again resplendent in a tux, but on the whole he'd rather have been at Stanford than emceeing the Concert for Young Americans at the D.C. Armory Starplex on Saturday.

"Where's George Starke and Mark May when you need them?" Riggins quipped as pianos and amplifiers were being moved around the stage. Absent an offensive line, Riggins moaned about having to perform "a cappella," groaned that the spotlights were starting to give him a suntan and confessed he couldn't sing "Hail to the Redskins" because he didn't know the words. "I thought I wanted to be a performer, but I'm beginning to change my mind."

Saturday's concert, which featured Johnny Lee, Jerry Lee Lewis and Kool and the Gang, was aimed at the 18-to-30 constituency that gave President Reagan surprisingly strong backing in the recent election. About 7,500 of them came, a number accompanied by chaperons. There was no dress code for this event, so there were equal amounts of black tie and blue jeans. While there were some full-length furs, most of the fur tended to be either around the collar or on boots. This was a good Republican cloth-coat crowd, and the only sparkles came from battery-powered Reagan-Bush buttons.

Still, this night in the shining Armory was the right party for the right parties. It may have been a concert, but 16-year-olds Susie Painter, Mandy Christopher and Jim Kernodle from North Carolina were having a ball. In town with their high school marching band for today's ceremonies, they weren't bothered by the cold. "It's hot up here!" they said.

Between sets, the two giant screens flanking the stage cut to the Presidential Gala at the Convention Center, with the presidential image eliciting cheers and applause every time it appeared. Much of the Armory crowd stood while Ray Charles rendered his version of "America the Beautiful," some singing harmony half a town away. When the president made his remarks at that concert's end, surrounded by Frank Sinatra, Mikhail Baryshnikov and other stars, Dan Boekenoogen from St. Joseph, Mo., said, "That's why it's $200 a ticket." Tickets for the Armory show went for $25.

When Kool and the Gang finally hit the stage after 11, the furs started flying out the door, but the young at heart headed for the front and for the aisles to celebrate Wheeee! The People. The night's only complaint came from two students up for the celebration from Davidson College in North Carolina. "Too much crowd control. What they ought to do is clear this out, set up kegs, have one price and have a big fraternity party. It's hard to meet people and there's a lot of people . . . There's fifteen of them right there, " said one, pointing to a group of college women, "but they have chaperons. We're going to Georgetown after this."

Not all the young were partying. Some were working. The Children's Express News Team -- Leigh Stein, 12, of California, Shana Burg, 16, of Massachusetts and Omri Elisha, 12, of New York City -- had cornered press volunteer Al Mendelsohn in the hallway and were questioning him about why beer was being sold at a concert for Young Americans (young is relative, he explained, particularly to Republicans), and, more specifically, about reports of underage kids buying beer at the concession stand.

"I would not be shocked if there was an occasional person who could pass for 18. It's dark in there," Mendelsohn conceded under the unwavering Geraldo Rivera-like gazes of the News Team, "but I think by and large everybody stuck to the drinking laws. I haven't had a drink all night . . . "

After his little session with Children's Express (their work is syndicated by UPI), Mendelsohn looked like he could use one.