WASHINGTON (Reuters) - Republican presidential candidate Herman Cain on Sunday said he was not promoting smoking in an ad that showed his chief of staff puffing on a cigarette.

The ad stirred much debate over what message it was trying to convey. Cain, on CBS' "Face the Nation," said there was no subliminal signal intended.

"One of the themes within this campaign is let Herman be Herman. Mark Block is a smoker, and we say let Mark be Mark," Cain said referring to his chief of staff. "That's all we're trying to say, because we believe let people be people. He doesn't deny that he's a smoker."

Cain, a former pizza executive, said the ad was not intended to glamorize smoking or offend anyone.

"We weren't trying to say it's cool to smoke," he said.

CBS "Face the Nation" host Bob Schieffer, a cancer survivor, in an unusual airing of his own opinion during the interview told Cain it did not serve the country to show someone smoking a cigarette.

"And you're the frontrunner now. And it seems to me, as frontrunner, you would have a responsibility not to take that kind of a tone in this campaign," Schieffer said. "I would suggest that perhaps, as the frontrunner, you'd want to raise the level of the campaign."

Schieffer told Cain to tell young people not to smoke.

"Young people of America, all people, do not smoke. It is hazardous and it's dangerous to your health. Don't smoke. I've never smoked and I have encouraged people not to smoke," Cain said.

(Reporting by Tabassum Zakaria)