Warren Sapp is FURIOUS with Hall of Fame voters for snubbing Terrell Owens -- and says Randy Moss could be in serious trouble if candidates are being judged by off-the-field behavior.

Sapp -- a Hall of Famer himself -- says he's "up in arms" about the Owens situation because the guy is clearly one of the best WRs of all time ... along with Moss.

But with Owens not getting enough H.O.F. votes for the 2nd year in a row, Sapp clearly believes he's being wrongly punished for his off-the-field antics.

Sapp warns, "What do we do next year when Randy Moss is standing there?"

Of course, Moss also had major off-the-field issues during his NFL career -- including a 2002 arrest for allegedly striking a cop with his car (he later pled guilty to misdemeanor traffic violations).