Much of the political opposition to the plan will focus on small-business owners, who are more sympathetic figures than rich investors and people whose jobs pay a lot.

“Struggling middle-class families need jobs, and small businesses cannot afford to hire more workers while paying higher taxes,” House Minority Whip Eric Cantor , R-Va., said in a statement.

Indeed, much of the revenue from partnerships, sole proprietorships and other small businesses flows to the people at the top of the income scale.

But a lot of the revenue generated by the surtax would come from other sources, including the effective limitation on deductions and an increase in the amount of revenue from capital gains, which also go into calculating adjusted gross income.

The taxes on investments are probably the single biggest factor. In 2006, for taxpayers with adjusted gross income over $1 million, capital gains and dividends made up 43.8 percent of income, compared with 11.5 percent for all taxpayers.

The White House is still refraining from endorsing or attacking particular revenue proposals for the health care overhaul.

Obama’s statement upon the House bill’s release did not mention the surtax. Earlier in the week, however, he reiterated his campaign pledge to limit tax increases to people making more than $250,000.

Obama did not campaign on the cap on itemized deductions, but he offered it in his budget to pay for expanding health insurance coverage. The cap would mean that the maximum benefit from an itemized deduction would be 28 percent, even though income tax rates are slated to top out at 39.6 percent in 2011.

Taxpayers in the top bracket would still get the full income tax benefit of their deductions, but they would not be able to use state and local taxes, mortgage interest, or charitable contributions to reduce their surtax liability.

Ways and Means member Sander M. Levin , D-Mich., acknowledged that the proposal would have an impact similar to the deduction cap. But he noted that the proposals are different and that the surtax is steeply progressive.

The only income free from the surtax would be items that are not taxable, such as the value of employer-provided health insurance and income from tax-exempt bonds, along with “above-the-line adjustments” to income, such as moving expenses and alimony.

The surtax also differs from a regular rate increase because of how it treats long-term capital gains and dividends.

Those two classes of income, though subject to a special 15 percent top rate, are still included in adjusted gross income.

Obama already wants to raise that rate to 20 percent for the top two brackets in 2011. The surtax would come on top of that, meaning that the rate at the very top would be 25.4 percent.

As a percentage, that increase is much larger than the increase in taxes on ordinary income, said Clint Stretch, managing principal of tax policy at Deloitte.

“The income mix in those very high income levels tends to be much more dominated by investment income,” he said. “Wages as a share of income goes down, and it goes down pretty precipitously.”

The road ahead for the surtax is far from smooth.

“I’ve been listening to senators, and I haven’t heard any support for it,” said Sen. Ron Wyden , D-Ore.

Wyden has proposed capping the exclusion of employer-sponsored health benefits from income and replacing it with a deduction or a credit designed to encourage cost containment and provide a tax cut to people with less expensive plans.