Richard Grieco -- I'll Be in the SECOND '21 Jump Street' Movie

He was DISSED by producers in the first "21 Jump Street" movie, but Richard Grieco (who starred in the classic TV series) tells TMZ ... he WILL be involved in the sequel -- REDEMPTION!!!!!!

Grieco -- who played alongside Johnny Depp in the TV series -- was noticeably absent from the Jonah Hill remake ... even though Depp got a cameo.

But last night, Grieco was hanging out in a funky shirt at the Pantages Theater in L.A. ... and he simply explained ... NOBODY EVER ASKED HIM!

Despite the burn ... Grieco did tell us producers are making things right ... saying, "I'll be doing the sequel."