Mitt Romney and President Obama released dueling tax overhaul proposals on Wednesday, touching off a fresh election-year debate over the federal deficit and the taxes paid by wealthy individuals and companies.

Romney proposed slashing individual income rates across the board by 20 percent, to lower the top tax rate to 28 percent from 35 percent, as part of a broad attempt at a policy reboot this week aimed at winning over his party’s conservative base.

Romney’s plan would cut all existing tax brackets by the same proportion, including cutting the lowest rate to 8 percent from 10 percent, and limit deductions for higher earners. Romney would also abolish estate taxes and the alternative minimum tax, and lower the corporate tax rate from 35 percent to 25 percent.

Romney unveiled details of his proposal hours after Obama set forth his own vision for a major overhaul of the nation’s corporate tax code. Obama’s plan would lower the nation’s corporate tax rate to 28 percent. And Obama would boost overall revenue from corporate taxation by banning numerous deductions and loopholes that save companies tens of billions of dollars a year on their tax bills.

The current U.S. corporate tax rate of 35 percent is one of the highest in the world, but the abundance of loopholes and deductions enables many businesses to pay far less than that — or nothing at all. Companies in the United States pay almost half the taxes that companies in other rich countries pay, compared with the size of the economy, according to the Organization for Economic Cooperation and Development.

The president’s plan targets oil and gas companies for tax increases while promising special breaks for manufacturing companies.

And in a slap at U.S. multinational corporations that shelter profits overseas, Obama wants those firms to pay a minimum tax on their foreign earnings. He also wants to end tax breaks for companies that outsource and give new tax incentives to firms that move jobs back home.

Both tax proposals were unveiled hours before a key Republican debate in Michigan, where next week’s primary could either reestablish Romney as the clear front-runner or further scramble the field.

It is unclear how either plan would fare in Congress. Many Republicans have favored reducing taxes on businesses well below what either Romney or the president is proposing. But Republicans and Democrats alike have shown support for a tax strategy that reduces rates across the board while eliminating special-interest loopholes.

Romney’s new plan, which goes further than the blueprint he released last September, reflects the political pressure he has faced in recent weeks to offer bold policy prescriptions to help him beat back a fierce challenge on his right from former Pennsylvania senator Rick Santorum.

Santorum took aim at Romney’s proposal and accused him of copying proposals Santorum had already introduced. Santorum’s plan would lower the top individual income tax rate to 28 percent and reduce the number of brackets from six to two, leaving the lowest rate at 10 percent.

“Welcome to the party, governor,” Santorum said to applause at a rally in Tucson.

Romney’s advisers hoped to shift the campaign’s focus from social issues back to the more Romney-friendly economic turf. On Friday, Romney plans to detail more components of his economic plan when he delivers what aides are billing as a major policy address before the Detroit Economic Club at Ford Field, home of the NFL’s Detroit Lions.

As Romney rolled out his tax proposals at a rally Wednesday in Chandler, Ariz., Romney rebranded his economic agenda with a new banner that said, “Restore America’s Promise.”

The wealthiest Americans stand to benefit most from Romney’s new income tax rates, but Romney argued that his plan would help middle-income Americans above all. He said he would eliminate taxes on capital gains and dividends only for people making $200,000 or less, and those making more than $200,000 will face limits on their deductions for things like charitable contributions.

“I’m going to limit the deductions and exemptions particularly for the higher-income folks,” Romney said. “For high-income folks, we’re going to cut back on that, so that we ensure that the top 1 percent keeps paying the current rate they’re paying and more. We want middle-income Americans to be the place that we focus because it’s middle-income Americans who have been hurt by this Obama economy.”

Obama’s campaign officials quickly attacked Romney’s plan, saying he gives tax breaks to the top earners while instituting damaging cuts to programs that help the middle class.

“Unfortunately, Mitt Romney doesn’t understand simple math,” Obama campaign spokesman Ben LaBolt said in a statement. “He’s giving more tax breaks to millionaires and billionaires, raising defense spending to an arbitrarily high level, and lowering corporate taxes without explaining how he would pay for them. . . . The plans Romney is announcing today will only add to that sea of red ink. For all that business experience Mitt Romney touts, it’s odd that he didn’t learn how to balance his own books.”

Romney’s campaign officials insisted that the tax overhaul would not add to the deficit, but would not detail specific individual deductions or corporate loopholes they may target to offset any decline in revenue.

Glenn Hubbard, a top Romney economic policy adviser, told reporters the plan would spark more economic growth and investment in the United States by restoring “a sense of stability and certainty” to the tax system and removing “legitimate fear that many busi­ness­ peo­ple have today of very large future tax hikes.”

Hubbard acknowledged that Romney’s tax plan would lose money compared with current policy. Although he claimed that the plan would boost economic activity sufficiently to make up the lost revenue, that idea has been largely discredited by economists.

“Once again, Mitt Romney has demonstrated he understands the need to promote economic growth, jobs, and wages,” Hubbard said in a statement. “Cutting business taxes and marginal tax rates across the board is a key step. Coupled with his spending plan to rein in both the federal government’s claim on GDP and debt, this tax plan is bold and pro-growth. These plans stand in stark contrast to President Obama’s increase in the size of government and his plans to raise taxes on business owners.”

Obama’s proposal to raise additional tax revenue through corporate tax reform is notable because officials had earlier hoped that corporate tax reform would neither add to, nor subtract from, annual budget deficits.

Now officials are counting on corporate tax reform to make a modest but still significant contribution to deficit reduction. And Obama has become more assertive in his push to raise taxes to help keep spending and revenue in check.

Obama has not offered a detailed blueprint for overhauling the personal income tax code — also full of loopholes and deductions — other than calling for higher taxes on the wealthiest Americans. Such a blueprint is not expected to come before the November presidential election.

Staff writer Sandhya Somashekhar in Chandler, Ariz., and Felicia Sonmez in Tucson contributed to this report.