Richard Belzer -- SLAMMED By Jewish Org. Over Hitler Salute

Richard 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."