Lenny Baker, the personable rotundity who plays sax and sings tenor for Sha Na Na has been greasing up for pay for almost four years. Yet other than the little dab of Brylcreme before each show, he hasn't had to alter his character to fill his role as the jolly good humor man of the group.

"I don't have any character to work up for the show," Baker says. "In the fifties scene I'm the kind of chubby kid who was always dancing around smiling and laughing and having a good time. It's the same as I've always been except my hair's greased back. In a way I guess I put off good vibes--like the guy on the Ozzie and Harriet show who was in the fraternity with David and Ricky. That's my character. I don't change character when I go on stage."

Baker has been playing sax since he was 12 years old (he's now 27), and he concedes that music is his life. When he isn't playing for Sha Na Na, he's playing in jam sessions down on Cape Cod. Yet as much as music means to him, he doesn't see the Sha Na Na act as strictly musical.

"We're almost an event, at least we think of it that way," he says. "Certain bands can still get away with just playing, but we feel you have to do a show. Everybody wants to have a good time at our concerts. That's the key. People say to me aren't you a little sick of old rock and roll?' Yeah, I'm tired of it, but you walk out of that place and you see everybody smiling. They all had a good time. Too many musicians have forgotten, I think, that they're entertainers."

Baker, who once played with Sha drummer Jocko in a Boston surf band, The Pilgrims, puts entertaining above all else. He says that he gets jumpy and nervous before shows, from sheer eagerness to get on stage. And at the root of Sha Na Na'a success is this kind of feeling, combined with a real affection for the songs and routines that they perform.

"We believe in the fifties," Baker says. "In order to do what we do, we have to believe in it."

Since Sha Na Na became big on the concert tour one of the trademarks of the group's performances has been the large number of people in the audience who "grease up" and dress fifties. "There are several different reasons I think people do this at our concerts," Baker says. "One is that when they grease up, they become a part of the whole thing. For that time that they're there at the concert and they're greased and we're on stage, they're part of the 1950s, or what they think was the 1950s."

"For others it's a trip back to when they dressed like that. A girl goes and finds an old gray skirt with pink poodles on it or puts her hair like she used to put it. It's the whole nostalgia trip--that's why it's an event, because people want to become part of this for that night."

Audience participation plays a big part in the Sha Na Na performance. And Baker says that it is an important factor when the group is planning its shows: "You shift things around to see where they work best. If they don't work right, you lose your continuity in the show. Then you have to shift it back somewhere else. We have to have that continuity, we can't let that audience down, we've got to keep it going. Once you let an audience down you've got to get them back up again."

Baker describes the closing series of songs in the Sha concert as an example of keeping an audience up: "We go from 'Duke of Earl' to 'Rama Lama Ding Dong' to 'At the Hop'--just bam bam bam. We're out of there. Come back on for 'Rock and Roll Is Here to Stay.' Come back on--our encores are all up tempo until we've got them standing on their feet. And then we just go--bam--and let them down with "Lovers Never Say Goodbye' and they know it's over. It's like a play or anything else, you've got to peak it and let it down."

Sha Na Na makes a lot of whistle stops at colleges around the country. And Baker, who had a sporadic career at Northeastern and never did get his degree, feels that the campuses are radically changing. "Colleges seem to be back into having a good time," he says. "The fraternities are back. They were really big for a long time and then became unpopular when everybody became politically aware. It's gone back to a more happy atmosphere. It's fun to go to college again. For a while there everything was so serious that it wasn't fun--at least I didn't think so."

While Baker didn't find college fun, he is having fun now, playing a demanding schedule, enjoying himself, and giving people a good time. "This could go on forever," he says, "or it could end tomorrow." But you have to know he hopes it doesn't.