Chris Kattan just pled not guilty to DUI ... and in an unusual move, the judge ordered him to attend AA meetings.

TMZ broke the story ... Chris crashed his Mercedes into a parked car on the freeway last month after allegedly admitting he had taken Rx drugs.  Earlier that day he was totally out of it on an airplane.

Chris entered his not guilty plea Monday morning and the judge ordered him to attend 2 AA meetings per week -- as a condition to bail. It's odd ... because everything we've found about AA focuses on alcohol ... not prescription meds. And alcohol was not a factor in the accident.

It's also curious ... the judge didn't order Chris to abstain from meds or booze.