It's odd to hear a successful actor call his work a "day job."

Michael Cerveris, who's opening on Broadway Thursday in "Assassins," says it only because he has a higher passion: rock-and-roll.

"I just feel a tremendous freedom in music," he said. "It's something that's more personal to me."

Although he sees connections in the two types of performance, Cerveris said he tries to keep them separate, so that his music will be judged on its own. But if not for an acting role, he might have missed a rock career, while rock has advanced his theatrical life.

Slim and boyish-looking at 43, even with a shaved head, Cerveris has been acting since graduating from Yale. His big break came in 1992, when he made his Broadway debut in the title role of The Who musical "Tommy."

That was, of course, a show with rock music, and Cerveris was cast after performing "Young Americans" at his audition.

"I bet," he said, "that no one else who went in to audition for 'Tommy' brought a guitar and played a Bowie song."

The fact that he felt confident enough to do that was the result of a previous acting part.

Growing up in West Virginia, Cerveris had been interested in both theater and music, but when he went to college he chose acting. He was perhaps intimidated a bit by the image of his father, a performer and college teacher of classical music.

"I guess I had a pretty high idea of what a musician was," said Cerveris, who had had little formal musical training. "In college, I did take voice - I sang German lieder, Italian art songs. I guess that was my connection to my Dad's world."

After graduating, he came to New York, and then went to Los Angeles when he got a role in the TV series "Fame." He portrayed a guitar-playing rocker, and that, he said, reignited the old musical flame.

"I would go to clubs in Los Angeles, and see groups," said Cerveris, "and I thought, I can do what these people are doing. I began to take music more seriously."

Over the years, Cerveris has appeared as a singer and guitarist with both American and English rock bands, although not achieving the visibility - or income - he's had as an actor.

The most attention he's had as a rocker has been in the theater, with "Tommy" and then in the hit glam-rock musical "Hedwig and the Angry Inch," playing the lead role of the transsexual German singer. After joining the cast during the off-Broadway run, he opened the show in London and in Los Angeles.

Now, however, Cerveris has achieved a landmark moment as a singer-songwriter - the release of his first solo CD, titled "Dog-Eared." It's an album dominated by intimate, personal ballads - several have a folk quality — featuring Cerveris' voice and guitar.

"It's been well-received," he said. "It's been treated as the genuine article, an indie-rock release, not as a vanity project. It's just by someone who happens to be an actor, too."

As he plans for a New York club date next month, Cerveris has hardly neglected his acting career, which obviously means a lot more to him than the typical day job.

Thinking that he was being perceived too much as a musical-theater performer - his Broadway credits also include the musical "Titanic" - he recently acted in a straight off-Broadway play, "Wintertime."

"I'd always done things like Shakespeare, many more non-musicals than musicals," he said. "I told my agent, 'I don't want to do any more musicals for a while, unless a Sondheim show comes up."

And a Sondheim show came up.

Originally done off-Broadway almost 15 years ago, "Assassins," with Sondheim's songs and a book by John Weidman, asks the audience to look closely at the men and women who've murdered - or attempted to murder - presidents of the United States. Cerveris plays John Wilkes Booth.

"I've done a lot of reading and research on him," said Cerveris. "I don't think he was insane. He had a view of Lincoln that a large number of people had - Lincoln was surprisingly unpopular, even in the North - and he thought he had his reasons. He believed himself to be a patriot.

"What's exciting about the show is that it holds these people up to the audience, and says: Account for this. Why have these assassinations happened in this country? It's not for no reason at all."

Before "Assassins," Cerveris' Sondheim immersion had included productions, in Washington and Chicago, of "Passion" and "A Little Night Music." In the fall, he's going to appear in "Sunday in the Park With George" in Chicago.

During the "Assassins" run, meanwhile, Cerveris, on some of his nights off, will be picking up his guitar and, with a band, reverting to his rock-and-roll self. (He'll be at Tonic in lower Manhattan May 2.)

"I guess," he said, "I'll just keep straddling two worlds."

E-mail: feldberg@northjersey.com