20 Percent

Romney's plan would cut individual income tax rates by 20 percent, eliminate the estate tax and alternative minimum tax and reduce the corporate tax rate to 25 percent from 35 percent. The combination of those policies would reduce federal revenue by $5 trillion over the next decade, an amount Romney has pledged to make up.

Obama has said he wants to raise taxes for top earners and multinational corporations. He has said Romney's insistence on rate cuts would mean a bigger deficit or higher taxes for the middle class.

Increased taxes for middle-class Americans may be inevitable, according to Gary Hufbauer, a senior fellow at the Peterson Institute for International Economics in Washington, who also spoke at today's Bloomberg Government breakfast.

Unless spending on entitlement programs such as Medicare is significantly reduced, Hufbauer said, "you can't close the budget deficit without raising taxes in one shape or another on the middle class. It's as simple as that, and the arithmetic is extremely powerful."

Hufbauer said taxes most likely would be raised by limiting deductions.

International Taxation

Hodge and Hufbauer also said the U.S. needs to overhaul international taxation of domestic companies, something proposed by Romney. Under current law, companies owe U.S. taxes on profits they earn around the world. They receive tax credits for payments to foreign governments and don't pay the U.S. until they bring the money home.

Romney wants to adopt a so-called territorial tax system, under which companies would owe little or no taxes on their overseas income. Obama has said lower taxes on foreign income earned by U.S.-based companies would encourage them to send more jobs and investment overseas.

"We are beginning to see companies move abroad" to take advantage of lower tax rates in other countries, Hodge said. "The handwriting is on the wall: We have to move to a territorial system or we will further erode our global competitiveness."

Adding Up