President Obama’s secretary paid a higher income tax rate than he did, the White House said Friday, arguing that the disparity underscores the unfair nature of the U.S. tax code and provides an even greater argument for enacting Mr. Obama’s so-called “Buffett rule,” which would require millionaires to pay a minimum of 30 percent of their income in taxes.

Mr. Obama released his 2011 federal income tax return showing that he and his wife Michelle reported an adjusted gross income of $789,674 and paid $162,075 in total tax — an effective federal income tax rate of 20.5 percent after taking into account the amount they donated to charity, $172,130.

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After White House blogger Keith Koffler questioned whether the president paid a lower rate than his secretary, a spokesman for Mr. Obama confirmed to ABC News’ Jake Tapper that he indeed paid a slightly lower rate than his secretary, Anita Decker Breckenridge, who makes $95,000 a year.

White House spokeswoman Amy Brundage told ABC News that Ms. Breckenridge paid “a slightly higher rate this year on her substantially lower income, which is exactly why we need to reform our tax code and ask the wealthiest to pay their fair share.”

In his State of the Union speech, Mr. Obama pointed out that billionaire investor Warren Buffet’s secretary pays a higher tax rate than Mr. Buffet does to illustrate his point that the wealthy should pay at least 30 percent of their income in taxes.

Republicans have countered that wealthy Americans can volunteer to pay more in taxes if they are so concerned about the disparity in the tax code.