Britney Spears (search) hit the big time pushing a squeaky- clean image, but now she's hitting the bottle — in public.

Click here to view NYPost cover with photo of Spears.

It's the latest public-relations faux pas for Britney, who soared to fame claiming to be an innocent teenager who detested smoking and drinking, and vowed to stay a virgin until marriage.

First, there was her bizarre 55-hour marriage. Then, she got engaged to a love rat who dumped his pregnant girlfriend. But her latest stunt may be her most disturbing: drinking what appears to be mini-bottle of booze on a public sidewalk in broad daylight.

Witnesses said the spectacle began as the singer and fiancé Kevin Federline (search), a dancer, pulled up to a Santa Monica liquor store, hopped out and bought what looked like a mini-bottle of whisky.

Apparently unable to wait until she got home, Britney twisted the top off the bottle and gulped down its contents.

Next, in a stunning display of trailer-trash bravado, she chased down the "whisky" with a can of the popular energy drink Red Bull (search).

Witnesses said the 22-year-old blonde also looked like something the cat dragged in.

"I had to look twice. It didn't even look like Britney. Her hair was a mess and she looked like she was wearing [Kevin's] jeans, they were so long," one person said.

Leslie Sloan (search), Britney's spokeswoman, had no comment.