Image: Calculator © Corbis

As Congress and President Barack Obama head into an election year, tax reform has emerged as a key roadblock to lowering the nation's debt -- and ultimately reviving America's economy and competitive edge.

Beginning in the George W. Bush presidency and continuing into the Obama era, national spending and tax revenue have diverged dramatically.

"We are rapidly approaching a time when the tax system we have will be unable to support the government that we want," said Howard Gleckman, a tax expert and resident fellow at the Urban Institute. "It's being held together by bubble gum and baling wire."

Bush-era tax cuts, as well as long-in-place tax breaks, expire at the end of 2011. Meanwhile, other established tax provisions will remain hot topics (and fair game) into the election year, as political and ideological rhetoric increases over how to reduce the nation's budget.

We asked Gleckman, author of the Tax Policy Center's TaxVox blog, and Dean Zerbe, the national managing director at the Alliant Group and a former tax counsel for the Senate Finance Committee, for their take on these tax cuts and subsidies.

Read on to see the most endangered tax provisions.

Capital gains and the 'Buffett Rule'

Obama got a lot of attention in September when he rolled out a deficit reduction plan including his "Buffett Rule" -- that no one making more than $1 million should pay a lower tax rate than the middle class.

In targeting this income group (whose income averages about $2.9 million annually), Obama recognizes that they make most of their money from investments. A few of these very high earners make more than two-thirds of their income from capital gains and dividends, which are taxed at 15%, said Bob Williams on the TaxVox blog.

While current rates expire at the end of 2012, the Obama administration would raise capital gains rates even as it cuts rates on ordinary income. For now, rates continue at historic lows for long-term capital gains and dividends. For taxpayers in the 15% income tax bracket and below, the rate is zero. For those in the 25% bracket and above, the rate is 15%.

The prospects of the "Buffett Rule" becoming law, however, are weak, with strong opposition among congressional Republicans. GOP presidential hopeful Mitt Romney would drop the rate on gains and dividends to zero for most taxpayers, with those making more than $200,000 still having to pay 15%, Gleckman said.

Research and development credit for businesses

The research and development tax credit celebrated its 30th anniversary in September. The basic credit rate is 20% and expires Dec. 31. Historically, the credit has been extended for a year or two and sometimes was allowed to expire and be restored retroactively, said Gleckman.

Although the tax credit is popular, there's room for improvement, said the Alliant Group's Zerbe. For example, raising the credit and offering a higher rate for small businesses would be a good start.

Both the administration and Congress have proposed raising the R&D tax credit as well as the related alternative simplified credit, or ASC, a simpler way for businesses to calculate the credit. "It can be a life saver for a small-business owner," Zerbe said.

Click here to become a fan of MSN Money on Facebook

IRA charitable donation

Congress extended this popular provision through 2011, but it will lapse in 2012 if lawmakers don't act. Donors older than 70½ may contribute up to $100,000 of IRA assets directly to one or more qualified charities. While there's no deduction, the gift is excluded from income, The Wall Street Journal reports.

More broadly, deductions that wealthier taxpayers claim will continue to be targeted by Republicans and Democrats heading into 2012. The White House has said that most of the cost of Obama's payroll tax cut and other job initiatives would be covered by limiting the deductions claimed by wealthier taxpayers.