Tax breaks that for years have been periodically renewed by Congress are in peril as congressional leaders struggle to agree on a plan to head off the numerous tax increases and spending cuts scheduled to begin this week.

One- or two-year reauthorizations of the “extenders,” which range from a credit for business research and development expenses to a state and local sales tax deduction, are often routine. But over the weekend, Republican negotiators led by Senate Minority Leader Mitch McConnell of Kentucky attempted to use the tax cuts as bargaining chips, judging that Democrats want to preserve the tax breaks more than Republicans do.

By Sunday night, it appeared possible that some or all extenders might not be available to businesses and individuals when they file their 2012 tax returns.

A senior GOP aide described the Republican position on tax extenders as “nuanced” and dependent on a variety of factors. A Democratic aide accused Republicans of “playing games” with the provisions.

Even before the latest negotiations, there were signs of trouble for the variety of interest groups that have promoted individual tax extenders.

In early August, the Senate Finance Committee considered legislation (S 3521) that would retroactively renew tax breaks that expired at the end of 2011 and continue them through 2013 at a cost of $72.8 billion. Thirteen committee Democrats and six Republicans supported the bill, but five GOP senators voted against the measure. The dissenting votes demonstrated that Republicans can no longer be relied upon to rubber stamp tax cuts, which are now sometimes described as spending programs run though the tax code.

Skepticism about extenders has been especially evident in the House, where Ways and Means Chairman Dave Camp, R-Mich., has led an effort to reduce the number of temporary tax provisions. Earlier this year, Ways and Members were asked to privately submit their two favorite temporary tax breaks and one they would like to see dropped.

In addition to high-profile items like the research and development tax credit and a credit for wind energy production, extenders include narrowly targeted provisions such as a credit for maintaining regional railroads and accelerated write-off periods for property purchased by film productions and motorsports complexes.

Renewed for a year or two at a time, such tax breaks appear to cost the government relatively little. But they can yield millions of dollars in tax savings for particular businesses and have been attacked by critics as prime examples of corporate welfare.

Uncertain Prospects

Since there is still bipartisan support for most of the extenders, it would be a surprise if many were allowed to expire for an extended period. Nevertheless, this is an anxious time for lobbyists and others with an interest in the fate of specific provisions.

Bob Rapoza, the chief representative of a coalition that supports a tax break for low-income community development known as the New Markets Tax Credit, said Sunday evening he had first heard on Saturday evening that there was resistance to the extensions approved by the Finance Committee. “Since then, we’ve not heard much to be encouraging,” Rapoza said. “We have no sense or we have not been told that New Markets is a problem, but rather the question is at this moment in time whether the package can handle an extension of expiring provisions and whether there is time to cull the provisions.”

One concern for Rapoza and others is that lawmakers’ interest in a retroactive extension of expired tax breaks could wane if there is no agreement on a fiscal package by Monday evening. Even now, the retroactive extension of tax breaks would mean that federal tax dollars would go to businesses based on decisions that they have already made. Potentially, the appetite for rewarding past behavior could dissipate as the page is officially turned on 2012.