Romney, in an interview with CBS News Wednesday, said the Obama campaign tries to "completely misrepresent my point of view, along with why I'm in this race."
"This is a campaign, not about character assassination, even though that's what I think has come from the Obama camp by and large," Romney said.
Obama campaign spokeswoman Jen Psaki told reporters Thursday Romney "and his team have a tendency to look at the president and make outrageous accusations about his truthfulness," but she said the Republican campaign has a "record of mistruths.
"If Mitt Romney were Pinocchio, his nose would be reaching from Virginia to Ohio, with the number of lies and untruths in the ads that his team has put out."
Romney and Obama both campaigned in Virginia Thursday.
Romney told supporters in Ohio Wednesday his tax-reform plan would probably not cut Americans' tax bills as much as they might be thinking.
"By the way, don't be expecting a huge cut in taxes, because I'm also going to lower deductions and exemptions," Romney told a crowd in Westerville, near Columbus.
"But by bringing rates down, we'll be able to let small businesses keep more of their money, so they can hire more people," he told the crowd. "My priority is jobs and I'll make it happen."
His campaign also backed away from statements Romney's tax plan would preserve most deductions for taxpayers whose adjusted gross income is less than $200,000 a year.
A staff member told The Wall Street Journal an alternative scenario would preserve those deductions for people who earn $100,000 or less, thus raising revenue by letting fewer taxpayers take deductions.
"What we're proposing is a tax reform -- it's not a tax cut," a campaign staffer told the Journal.
The staff member said the campaign hadn't committed to a plan, so things could change.
Romney has long proposed cutting all income-tax rates 20 percent and lowering the top corporate tax rate to 25 percent from 35 percent. He has said lower rates would spur economic growth.
He has also called for keeping the 15 percent top rate on capital gains and getting rid of capital gains taxes altogether for people making less than $200,000 a year. He has additionally said he would scrap the Alternative Minimum Tax and the estate tax.
The Tax Policy Center, a joint venture of the Urban Institute and the Brookings Institution, has said Romney can't do all those things without adding greatly to the deficit.
Several outside estimates have said Romney's tax plan could cut revenue by $5 trillion over 10 years, which would expand the deficit considerably.
Obama seized on this Wednesday.
"My opponent and his running mate are big believers in top-down economics," he said in Bowling Green, Ohio, near Toledo. "They basically think that if we just spend another $5 trillion on tax cuts that favor the very wealthiest ... then prosperity and jobs will rain down on everybody else, the deficit will magically go away and we will live happily ever after."
While Romney, a former Massachusetts governor, told reporters as late as last week, "I want to lower taxes on middle-income people," he told CBS's "60 Minutes" in a broadcast that aired Sunday that because he plans to limit exemptions and deductions, most people will essentially pay the same taxes as before.
"That's right. Middle-income people will probably see a little break, because there'll be no tax on their savings," he said.