WHERE would "Jersey Boys" be without the "Jersey Girls"?

The success of the world-beating Broadway musical about 1960s chart-toppers the Four Seasons may ultimately depend on the individual and collective talents of the male actors who portray the four musicians from North Jersey in the tune-filled, rags-to-riches story that's on the Forrest Theatre stage through Jan. 14. But without Kaleigh Cronin, Natalie Gallo and Ruby Lewis, there wouldn't be much of a production.

That's because, between them, the three twentysomething performers portray an astonishing 46 characters - from TV camera operators and hookers to waitresses and the members of the '60s girl group the Angels.

To put it another way, the costume changes come so rapidly, offered Manchester, N.H., native Cronin, "the guys in the crew all say, 'I don't know what you really look like.' "

For the record the redheaded Cronin is tall and willowy. Raven-haired Gallo, who hails from the Pittsburgh area, is shorter, while the equally petite, Kentucky-born Lewis is the trio's resident blonde.

All three women are appearing in "Jersey Boys" - whose national tour launched at the Forrest earlier this month - for the first time. All agree playing so many characters has made the experience different from their previous stage gigs.

"I've been in several ensembles. This is the most fulfilling" because of the challenges of undertaking so many roles, said Lewis. Her tally? Eighteen characters, among them Frankie Valli's old-world Italian mother and his doomed daughter, Francine.

Lewis added, "You'd be surprised to know how intricate the backstories of the characters are."

Generally, ensemble members in musicals appear primarily in crowd scenes and also may have one or two moments as dramatic characters scattered throughout a show, giving them plenty of down time. Not so with Cronin, Gallo and Lewis, whose backstage choreography likely rivals anything the audience sees. They all spoke of the seemingly nonstop action that occurs in the trio's stage-side, walk-in-closet of a dressing area where costume changes are sometimes achieved in a flash.

"The fastest change I do is 10 seconds, from an Angel to [Valli's wife]" said Gallo in reference to two of her 11 roles.

"I will sometimes come backstage and say, 'Who am I now?' " added Cronin. Her 17 characters include Valli's reporter-girlfriend and a call girl who's part of the entertainment at a post-gig party. "But someone will be there with the [correct wardrobe]."

In fact, Lewis described her work with the production's crack crew of dressers as being akin to "a pit stop at a NASCAR race."

Though some of their turns are barely cameos, all three women get to portray characters crucial to the play's various dramatic plots and subplots. Not surprisingly, each has found a favorite among her roles. For Gallo, that would be the late Mary Delgado, Valli's first wife.

"She was a sassy little one. I think we can all relate to that part of our lives," she said. "I would have loved to have met her and picked her brain."

Although Mary is written and surveyed by Gallo as a somewhat shrewish, tough-as-nails type (an attitude attributed to long absences caused by Valli's touring schedule), Gallo knows there's another side to her subject's personality. "People have said she was one of the most kindhearted women they've ever met," she said. "She was a very special woman. I try to remember that."

The character Lewis enjoys most is Valli's mother, mostly because she's such a stretch for the fresh-faced young blonde to play. "She's an older Italian woman. I have a lot of fun and try to find something different every night," she said.

Cronin's personal favorite is Lorraine, the journalist with whom Valli has an intense affair. "I spend the most time with Lorraine, and she's most essential to the story," Cronin said. Curiously, Cronin's also partial to her silent, fleeting stint bowling at an alley where an early incarnation of the Four Seasons is shown performing.

Their show's almost six-week Philly run is providing all three actresses ample opportunities to avail themselves of our city's varied pleasures. First-time visitor Cronin has so far concentrated on historical sightseeing, while Lewis, who has twice previously appeared on local stages, said she has "been taking advantage of all the great restaurants and art [galleries]."

But it's Gallo who seems to have made the deepest connection to the essence of Brotherly Loveville. Seeing the Rocky statue on the Philadelphia Museum of Art grounds was a highlight, she said, adding, "I checked out Pat's - and Geno's."