New York ? Christina Applegate 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,” 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.”‘

Applegate plays 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’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.”

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.”