WASHINGTON • Republican presidential candidate Mitt Romney and his wife, Ann, paid $3 million in federal taxes in 2010 on nearly $21.7 million of income derived from a vast array of investments, amounting to an effective tax rate of 13.9 percent, according to returns released by his campaign Tuesday.

In addition, the Romneys expect to pay $3.2 million on $20.9 million of income for the 2011 tax year, for an effective rate of 15.4 percent.

That's substantially lower than the top 35 percent marginal tax rate on wages and salaries — and much lower than the rate of his political rivals. President Barack Obama paid an effective tax rate of 26 percent in 2010, while former House Speaker Newt Gingrich paid a rate of 31.6 percent. Experts say Romney benefits from a tax code that allows investors to keep more of their income than wage earners, particularly investors in the rarefied world of private equity.

Even among his wealthy peers — a cohort that particularly benefits from the lower capital gains rate — Romney's rate is below the average 18.5 percent effective tax rate paid by the richest 1 percent, according to the Tax Policy Center.

"I pay all the taxes that are legally required and not a dollar more," Romney said in a debate Monday night. "I don't think you want someone as the candidate for president who pays more taxes than he owes."

On Tuesday, the Romney campaign released a statement from former IRS commissioner Fred Goldberg saying he had vetted the tax returns.

"These returns reflect the complexity of our tax laws and the types of investment activity that I would anticipate for persons in their circumstances," Goldberg said. "There is no indication or suggestion of any tax-motivated or aggressive tax planning activities. In my judgment, they have fully satisfied their responsibilities as taxpayers."

The longtime private-equity chieftain hopeful released his tax returns after pressure from Gingrich and at the urging of his political allies, who fretted that the matter was becoming a dangerous distraction.

The former Massachusetts governor has revealed in financial disclosure forms in the past that he is worth as much as $250 million, but he had never released tax returns that reveal how much money he makes each year — or how much he pays in taxes.

The release of Romney's federal tax returns may not provide dramatic new insight into his finances, but it is sure to fuel the increasingly high-decibel debate about economic disparity and tax fairness that has overtaken this year's presidential contest and repeatedly tripped up the Republican presidential hopeful.

Speaking on NBC's "Today" show Tuesday, senior White House adviser David Plouffe called Romney's taxes "a good example ... of the tax reform we need."

The intense focus on Romney's tax returns underscores how the very core of his candidacy — his experience leading a private equity firm — is also proving to be a liability in a political climate in which class issues have taken center stage.

Gingrich has been hammering Romney over his tenure at Bain Capital, while Democrats have taken to gleefully mocking the him as a modern-day Gordon Gekko, the high-flying financier portrayed in the movie "Wall Street."

Romney's returns show how much he has gained from paying the lower capital gains rate on much of his income from Bain, the private equity firm he co-founded in the mid-1980s.