You wouldn't expect somebody who has sung with the New York City Opera to have created the role of Rosie in "Mamma Mia!," but Judy Kaye gets around. She has been getting around professionally for more than 40 years, working in opera and cabaret, and with symphony orchestras, but mainly in musicals as varied as "Sweeney Todd," "Ragtime," "Grease," and "The Pajama Game." Right now, though, she is starring in Geva Theater Center's production of a play with music, "Souvenir: A Fantasia on the Life of Florence Foster Jenkins," playing September 8 through October 4.

As someone who has been performing professionally since 1968, Kaye doesn't believe in waiting around. "The most satisfying parts of my career have been leaps of faith," she says during a recent interview from her New Jersey apartment overlooking the Hudson River. When she got a phone call out of the blue to perform Leonard Bernstein's song cycle, "Arias and Barcaroles," she remembers wondering, "What am I getting into? But it exposed me to great material. It was unlike anything I thought I'd be doing, but I thought, ‘OK, why not.' Then you find out along the way why you said yes....I'm pretty much up for anything."

That also includes the part of Emma Goldman in the original Broadway company of "Ragtime," Rizzo in the first national tour of "Grease," one of the five daughters of four different Tevyas in "Fiddler on the Roof," and Mary Magdalene in five different companies of "Jesus Christ Superstar." She also started as an understudy in Cy Coleman, Betty Comden, and Adolph Green's 1978 musical, "On the Twentieth Century," but when leading lady Madeline Kahn had to withdraw after two months, she played the part for the rest of the 449-performance run. More recently, she played Mrs. Lovett, baker of the worst meat pies in London, in a New York revival of "Sweeney Todd."

Still active in what has been an unusually busy and varied career, Kaye says she prefers the theater: "At the base of it, I'm an actor with a character to play. When I sing, I even love the small plays inside songs." Not surprisingly, that approach informs her choice of songs for herself. "I look for something I can say with it. If I can find my way into it, I can make it my own even if great singers have performed it." Like so many singers of classic popular music, she says she pays particular attention to the lyrics. "If the words are right, the music takes care of itself." She names Judy Garland, Lena Horne, and Rosemary Clooney among many favorites, and among songwriters, George and Ira Gershwin, Irving Berlin, and Harold Arlen.

And that leads to the first question: Kaye has an admirable reputation among theater professionals and sophisticated audiences, so why Rochester? The big-time acts that come through here are usually rockers who pause long enough to work up a one-night sweat. The professional actors, regardless of how good they are, are usually short on name recognition. Yet after playing the part of Jenkins in the original New York productions in 2005, Kaye is now doing a limited tour to cities like San Francisco and Baltimore-and Rochester. She says, "It's a wonderful play and I'm not done with it yet. It's rare to have a part that suits the actor as well as this suits me."

The second question pertains to the play, itself, in which Kaye portrays the real-life Jenkins, a wealthy opera lover who was nothing if not confident. She studied seriously, performed, and made recordings. Except she was god-awful. Every note was sharp or flat, every tempo wrong, but she kept at it until she died in 1944 at the age of 76.

Kaye says singing badly isn't as easy as it sounds: "Anybody can sing badly-once. But you need to be good, and trained, to do it eight times a week without hurting yourself. Florence needs to be a believable bad singer, not somebody who squawks. We've worked out a lot of finely etched moments because I can't be surprising my accompanist."

She also believes that this is less a play about a person with the money to indulge her fantasies than an exploration of a relationship between Jenkins and her one true friend, her accompanist Cosme McMoon. Despite that odd name and the teeth-clenching singing, audiences have to care about their friendship.

One of the main differences between performing in a cabaret and a theater is the size of the room. "In a truly large space," Kaye says, "you dig in your toes and let it fly," but a small theater like Geva's, with its thrust stage and only 552 seats, is more like a cabaret than one of those musical barns they've built on Broadway in recent decades. A certain amount of intimacy is possible, the kind that lets a singer "investigate the material from inside out." Kaye adds, "You have to make it feel as if you're one-on-one with each person."

"Souvenir" runs through October 4 at Geva Theatre Center, 75 Woodbury Blvd. For information or tickets call 232-4382 or visit the website.