FAME-hungry BRISTOL PALIN fears a video showing her using drugs will ruin her bid to relaunch her showbiz career on DANCING WITH THE STARS!

The 21-year-old single mom is desperate to boost her brand with a second stint on the reality TV competition, insiders say, but she’s terrified the video will ruin her comeback.

“The video was shot in 2006, and Bristol is scared to death that it will surface now,” a source close to her told The ENQUIRER.

“Since the first time she was on ‘Dancing’ in fall 2010, Bristol has lost a lot of weight and had plastic surgery on her jaw line. She’s ready for her close-up, but if that video comes out, it would destroy her!”

The existence of the scandalous video – which allegedly shows then-15-year-old Bristol smoking marijuana – was revealed by The ENQUIRER in a world exclusive report in September 2008. At the time, her mother Sarah Palin, then governor of Alaska, had just been tapped to run as vice president alongside Republican presidential candidate John McCain.

“The video was filmed right before Bristol’s mom became governor,” revealed a friend who attended the house party in Wasilla, Alaska, where Bristol was caught smoking on camera.

“Bristol was parting like a rock star, as usual, and one of our pals was videotaping everyone as they drank and got high.

“At one point, he gets to Bristol and one of her friends holds the pot pipe to Bristol’s mouth and says out loud, ‘And here’s the future governor of Alaska’s daughter!’

“Bristol smiles at the camera, puts her lips around the pipe and inhales deeply. She holds in the smoke for a while, exhales, coughs a few times then laughs uncontrollably.”

The people who own the tape “have threatened to sell it before,” a former friend of Bristol’s told The ENQUIRER. “Now they’re thinking about shopping it again.”

And the timing couldn’t be worse for Bristol,  whose son Tripp with ex-boyfriend Levi Johnston is now 3.

Although she placed third in the 11th season on “Dancing” and her memoir “Not Afraid of Life: My Journey So Far” sold well, her Lifetime reality show “Bristol Palin: Life’s a Tripp” flopped so badly it was yanked from its original primetime slot after its second week!

Worse yet, Bristol’s fellow “Dancing with the Stars” competitor, Kyle Massey, filed a lawsuit against her reality show claiming that producers stole his idea.

A move to Arizona for Bristol – who is teaming up with pro Mark Ballas on “Dancing” – also turned out to be short-lived.

“With her previous ventures failing miser­ably, this could be it for Bristol,” warned the source. “To have her ‘drug party’ tape finally come out would send her back home to Wasilla in shame!”