A blonde walks into the White House and meets Interior Secretary Gale Norton: “I really like what you’ve done with the place,” she says.

The punch line, reported in Teen People, comes from Jessica Simpson, though it’s open to conjecture whether the singer-turned-reality-star-turned-uber-product-pitcher is really a ditz or just plays one on TV.

Either way, the popularity of her MTV series “Newlyweds: Nick and Jessica” has made the dazzling blonde America’s most popular dim-bulb since Suzanne Somers played Chrissy on “Three’s Company.” The MTV show follows Simpson’s married life with pop star Nick Lachey.

It’s hard to imagine “Newlyweds” would be such a cult hit without its famous “Jessica Moments,” when the reality-challenged pop star attempts to go camping, pump gas or discern the origin of Buffalo wings or Chicken of the Sea.

Is it an act?

“People call me a dumb blonde and to me, that’s funny,” Simpson says in a phone interview that she conducts while getting her hair and nails done. “I am ditzy and I have been since I was a young girl flirting with boys.

“I always played into it because it’s fun. That’s me showing my imperfections that people can relate to, so they know I’m not perfect.”

Rather than ditzy or dumb, there’s another word Simpson uses to explain her appeal:

Real.

“Whenever you have an image, it always hurts you,” she says. “Your image should be your heart and who you are. It shouldn’t be your costumes and this dance move or that dance move, or how you can shock somebody.”

Simpson is content to leave the shock tactics to Britney Spears and Christina Aguilera, singers who once overshadowed her in the teen-pop arena. Like them, Simpson auditioned for the 1990s version of “The Mickey Mouse Club” in Orlando, but she didn’t make the cut.

Instead, the Dallas native had her first career break as a contemporary Christian act, touring with Kirk Franklin, CeCe Winans and God’s Property. A preacher’s daughter, Simpson maintained that moral perspective even when she scored her first pop hit in 1999 with “I Wanna Love You Forever.”

When Britney and Christina were shedding clothes, piercing body parts and walking the aisle in Vegas, Simpson was keeping her virginity until her wedding night.

Now it seems like the approach might be paying off. Her wholesome image has made her ubiquitous in commercials for everything from pizza to breath mints. A new season of “Newlyweds” started Wednesday.

She reportedly is in line to play Daisy Duke in an upcoming big-screen version of “The Dukes of Hazzard,” beating out Spears.

If that triumph is sweet, Simpson isn’t gloating.

“I used to compete with people, and that was why my music was never successful,” says Simpson, 23. “I was always comparing myself to something else out there, so I was always feeling like I was not good enough. Being myself, that’s the best kind of success to have.”

Her easygoing manner separates Simpson from other stars who aim to be glamorous (Paris Hilton) or sexy (Britney), says one pop-culture observer.

“Jessica Simpson has really carved out an interesting niche in what was already a crowded cultural environment,” says Robert Thompson, founder of the Center for the Study of Popular Television at Syracuse University.

“Newlyweds kind of invented this other space for her,” he says. “She took a little bit from the book of Anna Nicole Smith with the obliviousness and cluelessness, but she’s so much more likable.

“With Jessica Simpson, you wanted to explain things to her and have her over for some pot roast. She’s inserting herself into the culture as almost this Gidget character who’s wholesome in her attractiveness.”

Simpson keeps it real at her concerts by taking questions from audience members and showing funny TV clips.

“It’s not about production,” she says. “It’s about me giving appreciation to the people who got me to the stage. I want people to relate to me.”

She adds that anyone who expects her to dish out dopey comments on demand when she’s out of the spotlight might be disappointed.

“They probably expect me to act that way, but five minutes into the conversation they’d probably say, “I’m pretty shocked.”‘

But not in a Britney way.