(Bloomberg News) Republican presidential candidate Mitt Romney's plan to reduce tax rates would need to be financed by ending widely used benefits such as the mortgage interest deduction, said Erskine Bowles, who was co-chairman of President Barack Obama's deficit-reduction commission.

Romney is "partly right and partly wrong" when he says he can cut tax rates by 20 percent and make up the money by curtailing tax breaks, Bowles said on Bloomberg Television's "Conversations with Judy Woodruff," airing this weekend.

"One area that Governor Romney is wrong is you can't just affect the top 15 percent" of Americans, said Bowles, whose bipartisan plan would cut spending and raise taxes. "It's just not enough money there in getting rid of the tax expenditures that only affect the upper-income people. You're going to have to affect people down through the brackets."

Romney and Obama are clashing over tax policy, with the president maintaining that Romney would slash taxes for top earners and the former Massachusetts governor saying his plan would unleash economic growth.

Romney wants to cut all individual income tax rates by 20 percent, pushing the top rate to 28 percent from 35 percent. He would lower the corporate tax rate to 25 percent from 35 percent, eliminate the estate tax and end taxation of investment income for people making less than $200,000 a year.

Broaden The Base

Romney, 65, said he embraces the concept of lowering tax rates and broadening the base that Bowles and co-chairman Alan Simpson used. There's one big difference: Bowles and Simpson want to use some of the revenue from curtailing tax breaks to reduce the budget deficit. Romney would dedicate all of the money to pay for lower tax rates and assume that faster economic growth would make up some of the difference.

Romney said he would make sure the tax code is as progressive as it is today.

"One of the absolute requirements of any tax reform that I have in mind is that people who are at the high end, whether you call them the 1 percent or 2 percent or half a percent, that people at the high end will still pay the same share of the tax burden they're paying now," Romney said on CBS's "Face the Nation" on June 17. "I'm not looking for a tax cut for the very wealthiest."

$5 Trillion