WASHINGTON — John McCain has asserted that his Democratic rival plans to raise taxes on anyone making more than $42,000 a year and will force all Americans into a "government-run" healthcare system. Barack Obama has accused the GOP presidential candidate of planning "the largest middle-class tax increase in history" and gambling with the Social Security earnings of millions of American seniors.

All these allegations, a sampling of charges traded back and forth on the campaign trail and in the three presidential debates over the past few weeks, are false.

During the final presidential debate yesterday, both candidates made their share of factual errors and distorted their rivals' positions. Obama again was misleading in describing the effects of McCain's healthcare proposal, while McCain again recycled the false assertion that Obama had voted to raise taxes on people making $42,000 a year.

Some of the sharpest back-and-forth over economic issues concerned the taxes that an Ohio plumber named Joe Wurzelbacher stands to pay under a possible Obama administration. McCain was correct in stating that Joe the plumber will end up paying a higher marginal tax rate under the Obama plan if his small business makes more than $250,000 a year. But McCain was wrong to say that Obama is planning to fine Joe the plumber and other small-business owners if they fail to provide health insurance for their employees.

While there is no evidence that today's candidates are any more untruthful than their predecessors, the explosion of media outlets and the rise of the Internet have made it difficult for fact-checkers to keep track of the fibs peddled by the rival political camps.

"It's like drinking from a fire hose," said Brooks Jackson, director of the Web site FactCheck.org, who has been truth-squadding presidential campaigns since 1991.

He said that McCain had "systematically misrepresented Obama's tax proposals over a long period of time," prompting Obama to turn around and do "the same thing" with the McCain healthcare plan.

"The big McCain deception about Obama is that he will tax everybody," said Kathleen Hall Jamieson, a professor of communication at the University of Pennsylvania. "But there is nothing in the Obama plan that can reasonably be described as higher taxes on people who make less than $250,000 a year."

McCain and his surrogates have repeatedly accused the senator from Illinois of voting to raise taxes on people making $42,000 a year, and suggested that this is a key part of the Democrat's campaign platform. The charge stems from the Democrat's vote in favor of nonbinding resolutions that assume, for budgeting purposes, that the Bush tax cuts will expire in 2011, as scheduled. Obama has promised to extend the Bush tax cuts for all but the highest-income groups.

Similarly, there is little to support McCain's charge that Obama would "force families into a government-run healthcare system where a bureaucrat stands between you and your doctor." The Obama plan is based on expanding the current U.S. system of privately backed health insurance.

The Obama campaign, meanwhile, has repeatedly mischaracterized the McCain healthcare plan as "the largest middle-class tax increase in history," in the phrase of a recent Obama television ad. While it is true that McCain wants to tax employer-provided health insurance for the first time, he is also promising a tax credit of between $2,500 and $5,000 to encourage Americans to buy their own health insurance. According to the nonpartisan Tax Policy Center, the tax credit will more than offset the higher tax for most Americans over the next decade.

As the Wall Street meltdown accelerated last month, Obama told Florida retirees that their Social Security earnings would have been "tied up" in the falling stock market "if my opponent had his way." While McCain has expressed support for a Bush administration plan to allow some Americans to establish "private retirement accounts," the proposal would not have applied to current retirees, and nobody would have been obliged to participate.

An even bigger question, economists said, is whether the election promises of either candidate are at all realistic at a time of rising international indebtedness and growing budget deficits. Both Obama and McCain have talked in general terms about the need for economic sacrifice but have shied away from spelling out what this will mean.

While McCain has talked about the need to eliminate earmark spending, and Obama has said he would increase taxes on the wealthiest Americans, "those are very small numbers" in relation to the scale of the problem, Steuerle said. The Tax Policy Center has projected a $459 billion deficit by 2012 under an Obama administration, and a $604 billion deficit under a McCain administration.