'Longmire' Star Deputy Ferg -- Busted for DUI ... JUUUUUST Over the Limit

Adam Bartley -- the lovable, bumbling Deputy Ferguson on "Longmire" -- just got a taste of his own medicine ... a skosh too much to drink landed him in jail for DUI.

Bartley was pulled over April 26th in Santa Fe, NM after a cop saw him driving a '93 Dodge pickup sans seat belt.

The officer says he smelled alcohol on Bartley's breath, and the actor folded like a cheap suit admitting he had "a few drinks."

Bartley performed poorly on multiple field sobriety tests ... so claim the cops. The breathalyzer was a heartbreaker ... .09, just over the .08 legal limit.

Bartley was arrested and charged with DUI, careless driving, and no seat belt.

"Longmire" originally aired on A&E. It got cancelled last year but it's since been picked up by Netflix.