Aaron Carter was spotted behind the wheel -- despite his claims -- before cops busted him ... this according to the police report.  

TMZ obtained the report, which contradicts Aaron's claim that cops never saw him driving, and therefore shouldn't have arrested him for DUI refusal in Cornelia, Georgia.

In the docs, a Habersham County Sheriff's deputy says he saw Aaron pull into the AutoZone parking lot after an alert went out for someone "driving all over the road and running into the median," in a white Chevy Suburban with no tags.

Aaron's rep says "the car was swerving because it was out of alignment not because he was drunk."

The deputy then approached him and observed his "eyes to be blood shot and watery with a glazed look to them." Aaron's girlfriend, cops say, then started acting belligerent.

During field sobriety testing, cops say Aaron talked to himself, lost his balance, swayed and had trouble tracking movement with his eyes.

Cops also say they observed "body tremors" in his legs and arms before he was arrested.