BEVERLY HILLS, Calif. — Four decades ago, Robert Morse starred as the young, up-and-coming advertising executive in "How to Succeed at Business Without Really Trying."

Today, Morse stars as Bertram Cooper, the senior partner of the advertising agency around which AMC's highly acclaimed "Mad Men" revolves. And, while he's aged 41 years between the two roles, he's still stuck in the '60s.

"The biggest change is that I never get the girl anymore," joked Morse, 77, who has a recurring role on the 1960s-era series. "I am the oldest person in the cast. And sometimes I have to hobble to the set.

"It is a strange thing coming in and seeing all of the young secretaries and knowing that I'm the Rudy Vallee part."

He's only kidding; he's not complaining.

"This is an astounding show," said Morse.

("Mad Men" airs Sunday at 8, 9 and 11 p.m. on AMC.)

And he's having fun with his character. Bertram Cooper is, well, unusual. It isn't normal for an American ad executive in 1962 to have an office decorated in a Japanese motif. Or to insist that people take off their shoes before they enter. Or to have a tendency to recommend that his subordinates read Ayn Rand novels.

Morse is quite clearly overjoyed to be a part of the show. He's like a fan who's dying to see the next episode.

"I go to table readings sometimes when I'm not in the show of the week just to hear it," he said. "And I'm not saying this to gloss it up. It is astounding the way the direction of the show is going in the second season. It's unbelievable."

Just don't ask him to elaborate.

"We are sworn to secrecy, and we have to burn our scripts," he said. (He was kidding about the script-burning. I think.) "We can't talk to our wives and our loved ones or anybody about what's going on, and we barely talk with one another about what's going on."

Clearly, he's extremely proud to be a part of a show that's gotten such widespread critical acclaim.

"I'm so grateful to be here with all of these people. And ... at my age, to be part of something that is absolutely magnificent," Morse said.

"I know everybody talks about their TV show as being the best and all of that, but I sincerely am very, very, profoundly lucky and thankful to be with all of these people and (creator/executive producer) Matt (Weiner) and the writers and the actors. It's a tremendous experience at this time in my life. And after "How to Succeed" and doing "Tru" and a one-man show, to have this opportunity."

And the opportunity to have some fun.

"I even come to work when I'm not working because I don't belong to a senior club," Morse joked. "So, I feel this is my club, and I come down to the set sometimes just to get the free lunch. And to be here with all of these wonderful people and hope that I'll be in next week's show."

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E-mail: pierce@desnews.com