ORLANDO, Florida — President Barack Obama warned Thursday that Mitt Romney’s “fairy dust” tax cuts would swell his millionaire Republican foe’s personal wealth while sticking the middle class with the bill.

In a punchy new personal attack ad running in battleground states, the Obama camp said Romney would hike taxes on families with children by $2,000 to pay for his $5 trillion tax plan that would mostly benefit the wealthy.

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“You work hard, stretch every penny,” the ad said, showing a picture of a man working at a desk and a woman comparing cans of tuna at a supermarket.

“But chances are you pay a higher tax rate than him,” the sonorous voice of the narrator said, as a picture of a smiling Romney, a former venture capitalist, flashed on screen.

“Mitt Romney made $20 million in 2010 but paid only 14 percent in taxes — probably less than you,” the ad said, branding the former venture capitalist’s approach as “He pays less. You pay more.”

The video was prefaced by footage of Obama walking along a colonnade next to the White House Rose Garden, and a voice-over of the president saying: “I’m Barack Obama and I approve this message.”

The Obama camp is using Romney’s bank balance, as well as his refusal to release more than two years of tax returns and complicated offshore accounting arrangements to paint him as out of touch with the hard-pressed middle classes.

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The new ad came on the eve of the release of new Labor Department employment figures, which, if poor, could boost Romney’s effort to savage Obama’s economic record and convince voters the president does not deserve a second term.

Obama based his assaults on a survey released by The Brookings Institution that said plans like Romney’s to lower rates and maintain tax breaks would spell “large tax cuts to high-income households, and increase the tax burdens on middle- and/or lower-income taxpayers.”

And the president linked Romney’s plans to the policies of the former Bush administration, which he blamed for setting off the economic crisis in the first place.

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“They have tried to sell us this trickle-down tax cut fairy dust before,” Obama said during a campaign swing to the battleground state of Florida.

“Guess what? It didn’t work then. It will not work now. It’s not a plan to create jobs. It is not a plan to reduce the deficit.”

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The Romney campaign rejected Obama’s attack.

“Under President Obama, middle-class Americans have experienced higher unemployment, lower incomes and greater uncertainty about the future,” said Romney spokesman Ryan Williams.

“Now he is promising to raise taxes on millions of families and small businesses — which is the last thing we should do in a struggling economy. “Mitt Romney’s plan for a stronger middle class will cut tax rates across the board and result in more jobs, higher take-home pay, and the kind of economic growth we haven’t seen under President Obama.”

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Romney has proposed cutting income tax rates by 20 percent, eliminating tax on investment income, getting rid of the estate tax and cutting the corporate tax rate.

The Republican’s campaign dismissed the tax study, describing its authors as partisan and saying it considered only half of Romney’s tax platform.

But the survey was prime ammunition for the Obama campaign’s contention that if elected, Romney would further tilt the economy toward wealthy Americans at the expense of middle class voters still suffering from the recession.

As Obama headed to Florida on Thursday, Democrats gleefully circulated a picture of the front page of the Tampa Bay Times newspaper bearing the headline: “Romney’s plan will hit middle class.”

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Romney paid an effective tax rate of 13.9 percent in 2010, according to returns he has released, because his income from investments was taxed as a capital gain rather than under high rates due for salaried income.