WASHINGTON (Reuters) - A proposal to impose at least 30 percent income tax on Americans making more than a million dollars a year will not hurt the economy by stifling investment and growth, U.S. Treasury Secretary Timothy Geithner said on Sunday.

"No credible basis for that argument, in my judgment," Geithner said on CBC's "Face the Nation."

"I don't think there is a plausible path to tax reform ... that doesn't recognize the reality that we cannot afford to extend these tax cuts for the most fortunate Americans," he said.

(Reporting By Lucia Mutikani; Editing by Sandra Maler)