Petula Clark didn't take to Norma Desmond right away. In fact, she recoiled from her the first time she saw her, when Clark was a teenager back in the 1950s.

The fictional Desmond, a fading, deluded silent-movie star, was being personified by Gloria Swanson in Billy Wilder's 1950 film "Sunset Blvd."

"I was too young when I first saw it. I thought it was spooky and weird," Clark said on the phone from Green Bay, Wis., where she's playing Desmond in a touring production of Andrew Lloyd Webber's musical adaptation from the film. It's opening Tuesday and playing through Jan. 16 at the Wang Theatre in Boston.

Clark is known primarily as the English pop singer who won two Grammy Awards in 1965 for "Downtown" and "I Know a Place," and another Grammy for "Don't Sleep in the Subway" in 1967.

She's perhaps lesser known as a film and stage actress who has appeared in such movies as Francis Coppola's musical "Finian's Rainbow" (co-starring Fred Astaire) and on stage in Willy Russell's "Blood Brothers."

A 60ish mother of three and grandmother of one, Clark, a child star called "the Shirley Temple of Britain," was in a Broadway audience when she next beheld Desmond being portrayed by Glenn Close. "I was not moved," Clark says. "The production was totally overshadowed by the set."

A few months later she got a call from Trevor Nunn, Webber's director, who "wanted to talk." Talk they did. "I spent what I can only describe as three grueling hours with him." He'd "made up his mind" that she was going to play Desmond in a touring production. "I didn't think I was right for it. I was a little scared of it. I'd seen Close. 'I wouldn't be like that,' I told him. 'Don't worry,' he said. 'You'll bring your own qualities of humor and vulnerability to it.' I hadn't thought of Norma Desmond in that way. 'Every actress who's played her has brought her own qualities to her and that's what you'll do,' he said."

Clark says that "you don't say no to Trevor Nunn," which is how she came to sign on. He told her not to look at the movie, an injunction she managed to obey until one night her son "tricked" her into looking at some of it on television. (On the other hand, Clark says, Nunn told Elaine Paige, another Desmond, to study the film closely. Paige wound up seeing it some 40 times.) When Clark looked at it with her son, she was so far into her character that she cried out against some of Swanson/Desmond's lines in the movie: "No, no, that's not what she's thinking!"

Clark debuted as Desmond in a London production in 1997, four years after it opened there. She has been touring the United States in this production since November 1998.

She's seen everybody who's played Desmond with the exceptions of Patti Lupone, Webber's original Norma, and Rita Moreno, who filled in when Clark took a break. Clark has now played the lead longer than any other actress, a field that also includes Betty Buckley and Diahann Carroll.

Clark says she's become so familiar with Desmond - starting with getting her American accent down - that "I don't feel I'm playing her any more." She describes the character as "one of the great roles for women."

She says her real-life reference for someone like Desmond is an acquaintance "who lives totally in the past, back in the '40s, in a time warp." Clark says Desmond is a "Hollywood creation, made and destroyed by it. If you totally dislike her, it's tough for you, because she's the centerpiece. She's a monster. She's not nice. She's deluded. She's rude. She doesn't see straight. But she can be funny, even dotty at times."

"I decided the way to play her was like playing Hamlet. Everyone who plays him brings his own qualities to him. That's what makes 'Hamlet' always different and interesting."

Clark concludes with the tour in May. She's working on an autobiographical one-woman show that she may try out in Ottawa or Montreal. It will have special effects and four singer-dancers accompanying her. "Not too many special effects," she adds. "I'm not big on special effects on the stage."