EXCLUSIVERichard Belzer's Nazi salute explanation isn't flying with a powerful Jewish group ... which claims the "Law & Order" star's actions were inappropriate, offensive and "not the least bit funny."
TMZ broke the story ... Belzer threw up the salute during a TV festival in Monte Carlo yesterday ... but insisted the gesture was not delivered in a "negative" way.
Belzer -- who described himself as a "Jewish comedian" -- said he was merely paying homage to the Charlie Chaplin movie "The Great Dictator" ... in which Charlie spoofed Hitler.
But the Anti-Defamation League isn't laughing ... in fact, ADL Director Abe Foxman -- a Holocaust survivor -- tells us, "Regardless of his explanation for his behavior, Richard Belzer’s imitation of Hitler was still inappropriate and offensive."
Foxman adds, "It’s not the least bit funny, but there’s no law against it. Someone who is Jewish should know better and not disregard Jewish pain and tragedy just for the sake of a joke.”