Luther Campbell To IRS -- Me Owe You Long Time

The 2 Live Crew song "Face Down Ass Up" pretty much describes the position Luther Campbell finds himself in right now ... because the Tax Man's about to rip him a new one.

Campbell -- famous for the 2LC hit, "Me So Horny" -- just got slapped with a $74K federal tax lien.

According to IRS docs -- obtained by TMZ -- Luther didn't pay either all or some of his 2012 taxes.

Campbell famously fought the government once before and won ... after a federal appeals court threw out a ruling by a lower court judge that the group's album, "As Nasty As They Wanna Be," was obscene.