Republican White House hopeful Herman Cain's "9-9-9" tax plan would leave 84 percent of Americans poorer but provide a huge windfall for every citizen earning over $1 million, a study said Tuesday.

Taxpayers earning more than ê200,000 would be better off from Cain's bid to re-sculpt the US tax system if he enacted it in office, according to an analysis by the Tax Policy Center think-tank.

Those with earnings above the ê1 million mark would receive an average cut of ê455,000 at the same time as workers below the ê200,000 threshold -- the 84 percent -- would be left paying more in tax than at present, the study said.

Cain, the former head of the Godfather's pizza chain, has surged in opinion polls in the past two weeks to top the list of Republican challengers aiming to unseat President Barack Obama in November 2012 elections.

The "9-9-9" plan would replace all federal taxes with a nine percent flat tax on personal income, a nine percent flat tax on corporate earnings and a nine percent national sales tax.

The Tax Policy Center, a joint effort of the Urban Institute and The Brookings Institution, based its findings on Cain's public comments and documents from Fiscal Associates, a company that analyzed the "9-9-9" plan.

The research also found that Cain's proposals would make a negligible difference to the total US tax take.

"If fully phased in, the plan would raise about $2.55 trillion of revenues at 2013 levels of income and consumption, virtually the same amount that would be collected if current tax policy were in place that year," if 2011 tax laws, other than a payroll cut, were extended, the think-tank said on its website.

"However, the plan would raise about ê300 billion less revenue than would be raised by current tax law, under which most 2001-2010 tax cuts would have expires by 2013."

Cain clashed in a televised debate with his Republican rivals Tuesday over the plan, as he battled to sustain his surge in the presidential race.

In a noticeably testy TV debate, the plain-speaking Cain repeatedly insisted critics had not understood his proposals, in particular the nine percent federal sales tax.

"Herman, I love you, brother, but you don't need to have a big analysis to figure this thing out," said Texas Governor Rick Perry, the former frontrunner who is struggling to claw his way back after a poll slump.