Smith -- a former All-Pro linebacker -- was arrested early Tuesday morning on suspicion of DUI in Mission, Kansas ... after cops say he was speeding and illegally changing lanes.

Officials say they suspected Smith was drunk ... so they put him through sobriety testing -- which he bombed.

Police placed him under arrest and hauled him off to Mission Police Department ... where he was processed.

Cops say they tried to administer a breathalyzer ... but Smith refused.

Officials then issued citations to Aldon ... and after he posted bond, he was released to a friend.

This ain't the 1st alcohol-related incident involving Smith ... he's been popped for at least 2 other DUI's in the past.

His drinking got so bad ... Aldon checked himself into alcohol rehab last March -- and his former fiancee told us she feared for his life.