Isaiah Washington -- Raging in Gay Bar to Get the Word Out On New Film

Isaiah Washington's on a guerrilla marketing campaign to spread the word about his new movie to the LGBT community, and he went all in -- maybe not all in -- by partying at a legendary gay bar.

Washington hit up Rage nightclub in West Hollywood (one of the biggest gay bars in town) this past weekend promoting "Blackbird" with his co-star Gary LeRoi Gray. We're told he was drinking and dancing ... having a great time.

The irony can't be overstated -- Isaiah was famously fired from "Grey's Anatomy" for using a homophobic slur during a blow up with T.R. Knight.

To be fair, that was 8 years ago ... and sources connected to "Blackbird" tell us Washington's role in the film is "not about redemption" -- he really just feels strongly about the movie's powerful message. It's centered around a gay African American man growing up in a small town.

We're told Washington's been totally on board with the plan to promote in the LGBT community -- and it shows.