Senator Max Baucus, the Montana Democrat who is chairman of the Finance Committee, plans to put the credit back when the committee takes up the plan, at a one-year cost to the Treasury of about $3.3 billion. Ultimately, even Republicans believe he will prevail.

But for now, according to committee aides, Republicans who had favored the credit felt that they needed to unite against it for Mr. Romney’s sake.

President Obama’s re-election campaign has been using Mr. Romney’s announcement to pummel him in the swing state of Iowa, where wind power is a growing industry. Conservatives, however, have praised Mr. Romney’s position as a stand for fiscal rectitude and against corporate welfare.

The tax package, known as “extenders,” has wins for both parties. Senator Jon Kyl of Arizona, the second-ranking Republican, is expected to secure the inclusion of a longstanding, often-ridiculed tax break for Nascar track owners. He and Senator Orrin G. Hatch, Republican of Utah, also beat back efforts by Senator Charles E. Schumer, Democrat of New York, to enlarge the package with an expanded tax break for tuition and higher education costs, which was included in the 2009 stimulus law but is set to lapse.

But in its place, Mr. Schumer demanded — and got — inclusion of a $92 billion provision to stave off the expansion of the alternative minimum tax, a parallel income tax system intended to force the rich to pay more but which is encroaching on the middle class. That provision alone should ease worries about an economic crisis next year driven by a sudden increase in taxes, Mr. Schumer argued.

“Bit by bit, we are turning the fiscal cliff into more of a slope,” he said.

The two-year package would cost nearly $152 billion, but most of that cost was the one-year minimum tax “patch.” Other big-ticket items are continuing the research and development tax credit for businesses, allowing small businesses to write off investments, a deduction for state and local sales taxes for residents of states without income taxes, and extending an existing tax deduction for education tuition.

The package was pared back from 73 provisions to 49, at a saving of around $32 billion. Jettisoned provisions included the tax credit for ethanol production, a credit for plug-in electric motorcycles and three-wheeled vehicles, charitable deductions for computer and book inventories and a credit for extracting more energy from depleted oil wells.

Senator Tom Coburn, Republican of Oklahoma, is moving to scale it back much further, with 61 amendments to eliminate or limit dozens of tax breaks, including deductions for mass transit and parking benefits, tax incentives for investments in low-income neighborhoods, the District of Columbia and the Gulf Coast, and tax breaks for film and television production.