WHOLESOME SINGER Olivia Newton-John says she knows exactly who to blame for persistent rumors she’s a lesbian — Johnny Carson.

The squeaky-clean “Grease” star — who, ironically, plays a lesbian ex-con in her new film “Sordid Lives” — has been dogged for years by constant whispers of flings with female friends.

But the Aussie songbird insists she’s 100 percent heterosexual and thinks the rumors were first sparked by an appearance on “The Tonight Show” in the 1970s.

“I’m in my little white pretty dress, and I sit down with Johnny, and he asked me some questions,” the 52-year-old beauty recalled in an interview. “And then he said something like, ‘Do you have more girlfriends or boyfriends?’ And I said girlfriends . . . female friends. And he did one of his only-Johnny-could-do eyebrow-raise kind of things.”

Ever since, Olivia has been the focus of gay gossip even though she’s been married, had a child and been linked with handsome studs.

A longtime pal told The ENQUIRER, “Olivia always knew about the rumors, and they didn’t really bother her.”

But, said Richard King, director of the Sydney Mardi Gras “2001: A Queer Odyssey” Film Festival: “I think her popularity with lesbians will certainly pick up after ‘Sordid Lives.'”

In the darkly comic film, the angelic Aussie plays Bitsy Mae Harling, a tattooed ex-con who had a red-hot lesbian affair with a Texas granny before she met an untimely death.

According to her Australian management firm, Olivia took the part because “it’s such a step away from her wholesome image.”