Tiffany Haddish has pleaded not guilty in her L.A. DUI case -- mirroring her plea to the same charge out in Georgia.

The comedian was arraigned Wednesday, where she entered "not guilty" pleas to two counts brought by the L.A. County District Attorney's Office -- driving under the influence of alcohol and driving with a .08% BAC.

TMZ broke the story ... TH was arrested in Beverly Hills last month, when cops claim they found her asleep at the wheel -- with her car partially blocking the road.

Tiffany joked about it the day after in a stand-up comedy set, but now it looks like things are getting serious ... 'cause she pleaded not guilty to the charges here AND in Georgia, apparently signaling that she's gonna fight.

The Georgia case was actually supposed to go trial this month, but it's been postponed. In court docs for that case, Tiff has reportedly alleged the cops there in GA conducted an unlawful search of her vehicle ... and she's also asked that her blood test result not be allowed as evidence.