EXCLUSIVE

Amanda Bynes has officially been charged with DUI after her arrest back in April -- when she sideswiped a cop car and allegedly attempted to flee the scene.

Bynes has been charged with one count of misdemeanor DUI -- and the D.A. has sought a sentencing enhancement because the actress refused to take either a breathalyzer or a blood test.

Bynes has not been charged with hit-and-run.

If convicted -- with the sentencing enhancement -- we're told Bynes faces a minimum of 48 hours in jail ... and a maximum of 6 months.

But because of jail overcrowding, it's unlikely Bynes will ever serve longer than a few hours.