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Christina Applegate (search) is making a leap, a big one. And it's not just during the dance numbers created for her by choreographer Wayne Cilento.

The actress, best-known for playing the bimbette daughter on TV's "Married ... With Children," is starring in a revival of "Sweet Charity," (search) opening April 21 on Broadway after an extended tryout tour.

"It had nothing to do with my career, my public or anything else," she says during an interview in the sleek, 42nd Street offices of Clear Channel Entertainment, one of the show's producers. She's talking about facing a New York theater audience for the first time.

"This needed to happen for me to become a better person, a better artist. After talking to a lot of people I respect, it hit me: 'If I don't do this, I will regret it for the rest of my life.'"

The actress says this calmly, deliberately, during an afternoon lunch break, sitting in an antiseptic, anonymous corporate lounge that looks westward to the Hudson River.

At 33, Applegate appears 10 years younger. The skin is flawless. The blond hair a bit tousled. Wearing jeans, a stylish T-shirt and a maroon scarf wrapped around her neck, she ignores a package of sushi as well as the bottled water placed before her.

Applegate is talking about Charity Hope Valentine, the goodhearted taxi dancer at the center of the Cy Coleman, Dorothy Fields, Neil Simon musical. It's not an easy role for a neophyte theater performer. Charity is a killer part, one that has to carry the whole show. No Charity, no musical.

In the past, "Sweet Charity" has attracted an impressive parade of women in the title role, starting in 1966 with the legendary Gwen Verdon, directed by the equally legendary choreographer Bob Fosse. Juliet Prowse was Charity in London. Shirley MacLaine starred in the 1969 film version. And dancer-choreographers Debbie Allen and then Ann Reinking were in the 20th-anniversary Broadway revival in 1986.

Applegate's theater experience is barely a blip, but that didn't stop producer Barry Weissler, the man behind the revivals of "Chicago" and "Wonderful Town," from hiring her.

"She has all of the qualities we wanted for our Charity -- innocence, vulnerability and yet she's seductive," Weissler says. "She's a beautiful young woman, and we all fell in love with her."

Applegate did have to face some grueling tests to get the job.

"She was the only woman who got through the dance audition," said Cilento, who has the unenviable task of coming up with new choreography for a show indelibly stamped with the footprints -- and dance steps -- of Fosse.

"Her line readings were so honest that they just made the material fresh," he said.

According to director Walter Bobbie, this 2005 "Sweet Charity" -- the first with a post-Fosse generation of dancers -- won't be a slavish revival.

"We had the blessing of Cy (who died last November) and Neil over the past year," Bobbie said, explaining that both composer and book writer were willing to re-examine the material. "To see these two men -- at this point in their career -- take that on was an inspiration."

Not that Cilento, who worked with Fosse on "Dancin'" and "Big Deal," won't pay homage to the master. "We don't want to reinvent 'Sweet Charity' to destroy it. We want to create new life and to bring a new point of view to the show," he said.

Applegate's journey to "Sweet Charity" began with her audition for the movie version of "Chicago." A tape was made of her audition, and the actress feels that may have sparked interest in her for the stage role of Charity.

"I grew up with the film of 'Sweet Charity,' and I was obsessed with Fosse," Applegate recalls. She has been taking dance lessons since age 5, although she stopped dancing about 10 years ago. "I felt like I had missed the boat in not doing it professionally in New York, which is what I wanted to do as a kid. I wanted to do Broadway."

She had several meetings with Coleman, including one particularly intense, three-hour get-together in Los Angeles.

"He was really challenging me. He wanted to see if vocally I had the stamina to do this. It was a very hardcore work session, but it was wonderful," she says.

Yet after Applegate was offered the job, it took her several months to commit, because she has never lived outside of her Los Angeles neighborhood, where she makes her home with her husband, actor Johnathon Schaech, who recently played Judas in the TV movie "Judas Iscariot."

"This was about uprooting my life -- moving away from what was comfortable," she says.

Right now, Applegate is in Chicago, where "Sweet Charity," is undergoing revisions and changes on its way to New York.

The reviews in Minneapolis, where the musical opened earlier this month, suggested work needed to be done. The Star Tribune called the show "a splash but no smash," and said Applegate "stays pretty and perky for much of the musical, serving cuteness instead of character."

After the Chicago run ends March 13, "Sweet Charity" heads to Boston, March 18-26. Preview performances start April 4 on Broadway at the Al Hirschfeld Theatre.

Applegate was a child of show business. Her father, Robert Applegate, is a record producer; her mother is actress-singer Nancy Priddy. Her first commercial was done before she was a year old. She remembers doing radio commercials at the age of 3. "That's when I started to really enjoy this," she says, talking about her show-biz upbringing.

"I didn't have anything else to compare it to. That's just what I did: after school, I went to auditions or I went to dance class or I went on the set and I didn't go to school for a while. I've worked steadily since I was 13 -- 20 years."

If "Married ... With Children" brought her the most fame, she also did "Jesse," a short-lived sitcom on NBC and had a guest shot on "Friends," which won her an Emmy in 2003.

"Those shows will be with me forever, and that's OK," Applegate says. "Ten years ago, I might have had a different answer. I'm a grown-up now, and I value the training I had.

"People always ask, 'Do you want to get rid of it?' As if being on a sitcom was a bad thing. They are not easy to do, and it was a wonderful challenge. It's a wonderful gift to be able to do that every week. And they pay really well, too."

Plus her television shows were filmed before live audiences, a big help in her efforts to understand the relationship between performer and audience in her current role. "You are aware of them. When you are doing comedy, you have to be. Everything is about your relationship with them. It's about pulling them in."

The first time Applegate and the "Sweet Charity" company went through the entire show without stopping, she found it was hard and exhausting -- "one dance number going into another dance number, and I'm in every single scene."

But at the end, I thought, 'OK, I can do this. I'm not afraid of this anymore.'"