John McCain and Barack Obama, armed with a new independent study of their tax plans, are accusing each other of wanting to overburden working-class voters.

Obama and McCain are both trumpeting their tax platforms and economic proposals, as $4-a-gallon gas and other market news sours Americans' economic outlooks. The candidates are balancing economic discussions with speeches on Iraq and foreign policy.

The study they referenced this week was a preliminary report out of the Tax Policy Center, which concluded that while both candidates offer "substantial" tax cuts, those breaks benefit two different classes of taxpayers - and both plans drive up the deficit.

The report said McCain's plan would offer "huge" breaks for high-income households, and Obama's plan would offer more relief to those on the bottom of the scale.

But the campaigns used select passages to swipe at each other this week.

McCain's campaign on Friday seized on a line that found Obama's plan to eliminate income taxes for seniors earning less than $50,000 would actually raise taxes for nearly 10 million senior households.

"(Obama) believes, obviously, in big government and big spending and higher taxes," McCain said at a town hall meeting in Pemberton, N.J. "I believe exactly the opposite."

His campaign circulated excerpts from the Tax Policy report, stressing that "in truth, his economic plan will be a disaster for everyone, especially seniors."

The hit was timed as Obama entered a meeting with seniors in Columbus, Ohio.

"I am convinced that if we do what Senator Obama wants to do, which is raise your taxes, that will be the worst and most harmful thing we can do," McCain said Friday.

But the presumptive Democratic nominee responded that his plan would still "completely eliminate" income taxes for 7 million seniors.

"On contrast, John McCain believes that senior citizens living on modest incomes should continue to pay taxes," Obama said in Ohio.

Obama referenced the same tax report a day earlier in Wisconsin, saying his plan helps more middle- and lower-class families than McCain's.

"I often say that John McCain is running to serve out George Bush's third term, but that's not being fair to George Bush," Obama said, claiming McCain was trumpeting even more "regressive" tax measures.

The new tax report does label McCain's plan as "regressive" and Obama's as "progressive."

But the report states that both candidates are "overoptimistic" in their quest to balance the tax cuts by closing loopholes.

The report states that their non-health tax proposals would slash revenue by $3.7 trillion for McCain and $2.7 trillion for Obama over the next 10 years.

Before using the report to criticize Obama, McCain's campaign complained that it offered "incomplete analysis" of both plans.

The two candidates also traded fire on their Social Security plans Friday.

Obama said he would apply the Social Security payroll tax to annual incomes above $250,000, which would affect the wealthiest 3 percent of Americans.

He also criticized McCain for being open to letting taxpayers invest part of their Social Security payments in private investment accounts.

McCain said Obama was misrepresenting his position.

"I will not privatize Social Security," he said. "But I would like for younger workers, younger workers only, to have an opportunity to take a few of their tax dollars, a few of theirs, and maybe put it into an account with their name on it. That's their money."

Current retirees would not lose any benefits, McCain said.

Click here to read more on the candidates' tax plans.

FOX News' Mosheh Oinounou and Bonney Kapp and The Associated Press contributed to this report.