Also Starring : Mr. Hey Now : JEFFREY TAMBOR FINDS HIS NICHE SITTING IN WITH GARRY SHANDLING

Jeffrey Tambor has developed great respect for Ed McMahon. Now that he’s into his third season as Garry Shandling’s sidekick on HBO’s “The Larry Sanders Show,” he’s learned something of the art of, well, just sitting there. “Basically, your whole job is to support,” says Tambor, whose previous series included “Max Headroom,” “American Dreamer,” “Mr. Sunshine” and “9 to 5.” “It’s a great responsibility to stay focused, to know when to talk, to know when to take it. And mostly, you have to listen.”

Tambor, with his balding head and familiar face, is one of those character actors people have recognized for years. But it’s the role of Hank Kingsley on the hippest cable series around--which takes us backstage at a late-night talk show--that has really locked him in many viewers’ minds. “I just did a film in North Carolina,” Tambor muses, “and even there, people at the stores were yelling, ‘Hey now!,’ his character’s signature phrase.

The actor feels it’s Kingsley’s many facets, his unpredictability, that hit home. Despite some arrogance and seeming buffoonery, there’s a lot more there. “All the characters on the show are layered, which I love,” he says. “My concept of Hank is that he’s an absolute professional as an announcer and an absolute amateur in life. And while he has a buffoonish aspect to him, you’re always wondering if he just wants to be seen that way to get off the hook.”

Those involved with casting Hank knew when Tambor first read that they had found their man. “Jeffrey is a very strong actor, and he’s turned Hank into someone you look forward to every week,” says Brad Grey, one of “Larry Sanders’ ” executive producers.

More of Hank’s layers will be revealed this season. “We’ll explore a darker side of Hank and you’ll have greater insights into how he thinks,” says Grey. Show fans will continue to see in Hank deeply rooted, and probably unfulfilled, ambition, a theme many can relate to. “Oh, I think in his deepest recesses he probably thinks he can do Larry Sanders’ job better himself,” says Tambor But that sort of naivete helps offset the times he can be a prima donna and a bit dismissive. He’s a guy who chooses when he’s aware and not aware.”

One thing Tambor himself was aware of was the obvious quality of “The Larry Sanders Show,” something apparent when he read the first script. At the same time, he was offered two other network series.

“I held out for this one,” he says, “because I just felt it would be successful. It also appeals to the voyeur in us. Everyone wants to know what David Letterman is whispering to a guest just as they go to commercial. Our show answers that question.”

After appearing in numerous network series that didn’t succeed, Tambor also has responded positively to working for a cable show.

“HBO keeps saying, ‘Kick it out, take risks,’ and so the show is irreverent. It will pass by many laughs to get to the one good laugh,” he says. “There’s a bit of danger to it. I’d truly rather be on cable, because the whole frame of reference, what you can say and not say, is greater. There’s just an attitude I like.”

A calm, unusually secure man out of character, Tambor harbors no bitterness about past failures on television, except one. “The only one I ever said, ‘Dammit, it’s too soon,” when it was canceled, was ‘Max Headroom’,” says the man who played newsroom director Murray in the cult 1987 show set in a TV-dominated future. “The show was way ahead of its time.”

Right now, everything feels completely in balance for the actor who lives with his wife, Katy, in Sherman Oaks (he has a 20-year-old daughter from a previous marriage). He reads voraciously, teaches acting, works out daily on the life-cycle in his office, makes movies in between shooting “Larry Sanders” (three this past year) and, basically, just loves this job.

“I think an actor gets maybe four or five roles in his life that just fit,” says Tambor. “Hank and I are both reaching our 50th year at the same time, and the merger works. And being on this set, there is so much laughter and a kind of randomness, sort of like a party. You feel like you work hard, but it doesn’t feel like hard work.”

It’s work he wanted from the age of 10 when, as a youngster, he would walk across the street from his San Francisco home to the local college and watch the theater department in action. “It just seemed very exciting to me,” he says, “to do things on stage that you could never do in life. There certainly was no history of show business in my family except that we are Hungarian Russian Jews. And with that comes a lot of theatrics.”

“The Larry Sanders Show” airs Wednesdays at 10:30 p.m. on HBO.