Lance Armstrong -- I'M DONE After 500+ Negative Tests for Doping!!

Lance Armstrong is through defending himself against allegations he cheated to win his Tour de France titles ... because he says he's already given 500-600 samples that were ALL negative.

Armstrong, speaking on Gavin Newsom's new late night talk show, says he's not even arguing with people anymore who think he cheated -- "I'm not wasting any more of my time talking about it and you shouldn't waste your time talking about it. Let's move on."

Armstrong is currently competing in triathlons, and says he believes most people already made up their minds about whether he was juicing during his string of 7 consecutive Tour de France victories.

Newsom's new show premieres on Current this Friday night.