Appearing on the "Late Show With David Letterman" Monday, the actor spoke live via satellite from Television City, Calif., and fielded questions from Letterman, while in-studio guest Jerry Seinfeld looked on.
"For me to be at a comedy club and flip out and say this crap…" said Richards. "I'm deeply, deeply sorry."
Earlier in the day, as news of Richards' comments hit the web, Seinfeld issued a statement saying he is "sick over this horrible, horrible mistake" and calling Richards' remarks offensive.
A video on TMZ.com shows the actor, 57, repeatedly yelling racial remarks at a man who sat in the audience at the Laugh Factory in West Hollywood. It apparently happened after someone in the crowd said he wasn't funny.
"Fifty years ago we'd have you upside down with a f------ fork up your ass," he says while on stage.
"You can talk, you can talk, you're brave now motherf------. Throw his ass out. He's a n-----! He's a n-----! He's a n-----! A n-----, look, there's a n-----!"
Some chuckling was heard coming from the audience throughout the outburst, along with gasps of "Oh my God!" and other exclamations as Richards veered into unprintable invective.
Eventually someone calls out: "It's not funny. That's why you're a reject, never had no shows, never had no movies. `Seinfeld,' that's it."
Monday night, Letterman asked Richards if he would have responded to the heckler in a similar vein if he had been of a different race.
"It may have happened," said Richards. "I'm a performer. I push the envelope. I work in a very uncontrolled manner on stage. I do a lot of free association — it's spontaneous, I go into character. I don't know. In view of the situation and the act going the way it was going, I don't know. The rage did go all over the place - it went to everybody in the room."
Richards seemed baffled by his own reaction on stage.
"I'm not a racist, that's what's so insane about this," he said.
The actor said that he went back to the club later that night and went on stage to "get back on the horse, as they say." He said he apologized to as many people as he could after the incident, but some of the people he targeted had already left.
He added that he supports the people who complained to the press about his comments.