BOCA RATON, Florida (Reuters) - President Barack Obama's campaign blasted Mitt Romney on Tuesday for not paying his "fair share" of taxes, escalating the rhetoric against the leading Republican presidential contender to try to paint him as an elitist who is out of touch with ordinary Americans.
Obama has made tax fairness a key part of his re-election message and he piled on the pressure by urging support for the "Buffett Rule" during a speech in Florida, which is likely to be a key battleground state in the November 6 general election.
Named after billionaire investor and Obama supporter Warren Buffett, the proposal calls for people making more than $1 million a year to be taxed at a higher rate than middle-class families.
Obama said this principle of fairness was in stark contrast to plans offered by his Republican opponents, whom he accused of looking out for the rich at the expense of the middle class.
"Lot of the folks who are peddling these same trickle-down theories, including members of Congress and some people who are running for a certain office right now, who shall not be named, they're doubling down on these old, broken down theories," Obama said in a clear swipe at Romney.
The wealthy Republican front-runner has virtually clinched the nomination to face Obama in November after conservative rival Rick Santorum suspended his campaign on Tuesday.
With the Democratic president seeking to appeal to blue-collar voters he needs to win a second term, the Obama campaign stepped up its attack on the presumptive nominee.
"Mitt Romney opposes the Buffett Rule. He thinks millionaires and billionaires should keep paying lower tax rates than middle-class families. In fact, Romney himself isn't paying his fair share," the Obama campaign said in a statement.
The criticism on taxes is the second assault against Romney in less than a week from the Obama campaign, as it becomes clear that the former Massachusetts governor is likely to be the Republican candidate in November's election.
"We've heard about the so-called Buffett rule, but what about the Obama rule? The Obama rule says that we must tax American families and small businesses so that government can grow," said Romney campaign communications director Gail Gitcho.
The attacks signal a start to the general election campaign after months of Republican primaries to settle on a nominee.
A Washington Post-ABC poll on Tuesday showed Obama would win a match-up against Romney by 51 percent to 44 percent. But Romney had a double-digit advantage among Americans when it comes to reducing the federal budget deficit, and a narrow edge on managing the economy.
"Four years ago, President Obama came to Florida running on 'Hope and Change' and it's clear now that that was just all an act. The president didn't change Washington, and he put in place policies that hurt our economic recovery," said Republican National Committee Chairman Reince Priebus.
FALLING ON DEAF EARS?
Obama's push on tax fairness may also be falling on deaf ears in the swing states where the election will likely be decided.
In 12 battleground states, 80 percent of independent voters lacking strong views on either Obama or Romney said they prefer a candidate who focuses on creating economic opportunity rather than reducing income inequality, according to a poll by the moderate Democratic group Third Way released on Monday.
One of the richest men ever to seek the White House, Romney's tax returns from 2010 and 2011 show he paid an effective tax rate of 14.5 percent during the two-year period.
Many of the wealthy pay at a lower rate because much of their income is from dividends, taxed at a 15 percent rate.
Obama, speaking in the affluent seaside town of Boca Raton during a trip on which he attends three fundraising events, said his push reflected an American tradition of fairness.
"These investments, in things like education and research and healthcare, they haven't been made as some grand scheme to redistribute wealth from one group to another. This is not some socialist dream," he told students and faculty at Florida Atlantic University.
A White House report released earlier on Tuesday found taxes on America's highest 400 earners have fallen sharply in the last 17 years, to 18.1 percent of their income in federal taxes versus 29.9 percent in 1995.
The Democratic-controlled Senate will take up the "Buffett Rule" on April 16, the day before the deadline for Americans to file income tax returns.
Even if it passes the Senate the measure is unlikely to make it through the House of Representatives where Republicans hold a majority. Republicans oppose the "Buffett Rule" and said Democrats were simply using it to try to distract voters from their failure to boost growth or curb high unemployment.
American Crossroads, the biggest Republican Super PAC, backed a Facebook petition calling on Obama and Buffett to pay more taxes themselves if they believe rates are too low.
"President Obama and Warren Buffett are deeply troubled about how low their taxes are. Nothing is stopping them from paying more in taxes voluntarily," the petition says.
(Additional reporting by Susan Heavey; Writing by Alister Bull; Editing by Alistair Bell and Christopher Wilson)