David Cassidy was just arrested by Tom Jones ... for drunk driving.
Law enforcement sources tell TMZ, Cassidy was in upstate New York early this AM -- outside Albany -- when he was pulled over by OFFICER Jones for driving with his high beams when he wasn't supposed to.
We're told Jones smelled alcohol on Cassidy's breath and administered a field sobriety test, during which Cassidy performed poorly. The singer/actor blew a .1 and was cuffed and taken to jail.
He now faces felony drunk driving because he had a prior DUI in Florida.
Cassidy has been released on $2,500 bail.
His stepmom, Shirley Jones, has said recently David is a troubled man who has demons he's been struggling to conquer.
12:50 PM PT -- According to the police report, Cassidy left his high beams on as he approached the checkpoint (always a tip-off to cops) -- and in addition to the breathalyzer ... he also "failed all" the field sobriety tests Officer Jones put him through.