And like most of the wealthy, the Romneys paid only a tiny sliver of their income in payroll taxes, which cut heavily into the weekly paychecks of wage earners but is barely a blip on the returns of the rich. While payroll taxes eat up 6 percent of the income of Americans earning the national median income of $50,221, Mr. Romney and his wife paid just one-tenth of 1 percent of their income in payroll taxes.

Mr. Romney’s 2010 returns also suggest he may have paid far less taxes the previous year. The 2010 return shows the family made estimated tax payments for 2009 of $1,369,095. To avoid penalties, estimated tax payments must be at least 110 percent of the taxes owed the prior year. Assuming that is what he paid, his federal tax bill for 2009 would have been $1,244,632, far less than in 2010.

Mr. Romney and other Republican candidates have not only opposed higher taxes on the wealthy, but also favor maintaining or expanding the relatively low rates for capital gains and investment income, breaks that Republicans and others favor as a way to spur investment and reward risk-taking but which critics say have fed the growing wealth gap.

Those reductions in taxes on investments began with a deal between Bill Clinton, a Democrat, and Mr. Romney’s chief rival for the Republican nomination, Newt Gingrich, then speaker of the House. They accelerated under President George W. Bush, who cut taxes on dividends and capitals gains to their current levels, and survived a push by Mr. Obama and the Democratic majorities in Congress in 2010 to restrict tax advantages for financial managers. Indeed, if Mr. Romney became president and won approval of his own tax proposals he would pay less in federal taxes than he would under current law.

Mr. Gingrich has proposed even steeper reductions, which would nearly eliminate Mr. Romney’s federal income tax burden. During the 15-minute conference call, Mr. Ginsberg argued that the documents should settle any lingering questions about Mr. Romney’s investments and tax burden. Mr. Romney’s tax return was “complicated — and it is also fully transparent,” he said.

But the documents suggest that the Romneys or the lawyer overseeing the family’s blind trusts, R. Bradford Malt, may have been sensitive to the political implications of at least some aspects of the family’s finances.

In 2010, about $3 million of the family’s assets were held in a UBS bank account in Switzerland. Mr. Malt said that the account complied with all Internal Revenue Service reporting requirements and that the family had paid all applicable taxes on the interest earned by those assets.