U.S. Olympic Skiier Julia Mancuso -- Check Out My Hot Butt Crack

Here's Team USA downhill skier Julia Mancuso trying to get America hooked on crack ... and it's working.

The 29-year-old Olympian -- who chalked up a gold medal at the 2006 Olympics in Turin -- threw on one of the lowest plunging catsuits ever for a sexy photo shoot for February edition of GQ.

Mancuso is considered America's best hope for Olympic gold in the speed events -- and she doesn't lack confidence. In fact, she brags on her Twitter page, "I ski better than you."

Hope she's right ...