Lady Gaga for ROLLING STONES

Watch out, Katy Perry: there’s a new princess of pop who kisses girls (for real), claims Marilyn Manson and Madonna as fans and is on the verge of becoming the defining pop star of the year. Lady Gaga struts the streets pants-less, has everyone from Weezer to Justin Timberlake singing her songs and has moved nearly 10 million digital singles — and now she’s on the cover of Rolling Stone’s annual Hot List.

“I don’t feel like I look like the other perfect little pop singers,” she tells RS‘ Brian Hiatt in our new feature, on newsstands today. “I think I’m changing what people think is sexy.” Gaga is also changing what it means to be a 21st century pop star, and she’s doing it through 24 hours a day of fierce work — she’s a walking Gaga art project known as much for her outrageous fashion sense as her Eighties-flavored dance hits. “The truth is, the psychotic woman that I truly am comes out when I’m not working,” she says (during Hiatt’s time with the star, she rocks a massive radio concert, takes advice from Cyndi Lauper at a photo shoot and suffers a brief breakdown at a Walmart.com taping). “When I’m not working, I go crazy.” (Track her eye-popping outfits in Lady Gaga’s Wild Looks: The New Princess of Pop’s Craziest Wardrobe Moments.)

Lady Gaga’s devotion to being a star drove her to order bags of cocaine and spend hours perfecting her hair and makeup in a tiny Lower East Side apartment after she dropped out of NYU several years ago — well before she was actually famous. “It was quite sick,” she admits. “I suppose that’s where the vanity of the album came from.” Her debut, The Fame, was almost entirely inspired by her relationship with a heavy-metal drummer named Luke, and their breakup profoundly changed Gaga. She tells Hiatt she’s bisexual, but her attraction to women is purely physical. It’s an aspect of her sexuality that makes boyfriends “uncomfortable,” she says.

Her sexuality proclivities don’t seem to offend Marilyn Manson, however, who lobbed a series of awful pickup lines at his new friend at our cover shoot (grab the issue to hear his worst). “She knows exactly what she’s doing,” he tells RS. “She’s very smart, she’s not selling out, she’s a great musician, she’s a great singer, and she’s laughing when she’s doing it, the same way that I am.”

The savvy Gaga reveals her real musical goals are serious, though: “My true legacy will be the test of time, and whether I can sustain a space in pop culture and really make stuff that will have a genuine impact.”

For much more on Lady Gaga — including her post-Wango Tango hangout with Perez Hilton, how she went from a posh prep-school kid to half-naked bar dancer, and her most vital influences — pick up our new issue, on stands today. And stay tuned to RollingStone.com for more special features from 2009’s Hot List