The Treasury Department said Tuesday it would begin tapping civil service retirement funds because Congress has not raised the federal debt ceiling, the latest reminder that time is running out before the government is at risk of defaulting on the national debt.

The action will allow the government to spend $156 billion that otherwise would have been invested in the federal Thrift Savings Plan. As a result of that action and others the Treasury is taking, Congress has until between mid-February and early March to raise the $16.4 trillion debt limit.

So long as the debt ceiling is raised on time, federal workers and retirees should not be affected.

The announcement that Treasury was tapping the federal retirement plan comes at the same time as several other developments regarding the debt-ceiling battle, which promises to dominate Washington right after next week’s inauguration.

President Obama says he won’t negotiate over the debt limit, while Republicans insist that the need to raise the debt limit offers a critical source of leverage to force deep spending cuts.

President Obama aggressively pushed his debt ceiling agenda on Monday during the final press conference of his first term. (JulieAnn McKellogg/The Washington Post)

On Tuesday, the University of Chicago’s Booth School of Business reported that more than 80 percent of the country’s leading economists say the nation’s debt ceiling creates unnecessary uncertainty and can lead to worsening the nation’s financial picture, according to a new survey of more than 40 academics.

The survey says 84 percent of the nation’s economists agree or strongly agree that a “separate debt ceiling that has to be increased periodically creates unneeded uncertainty and can potentially lead to worse fiscal outcomes” — because spending must already be approved by Congress and the president.

The survey, which periodically asks top economists about their opinions, reported that 3 percent of survey respondents said they disagreed with the statement and none said they strongly disagreed. When weighted by each economist’s confidence, 97 percent of the experts agreed with the statement.

The survey includes a range of economists with differing backgrounds and political inclinations.

In written responses to the survey, Angus Deaton, a Princeton professor, said the debt limit “does indeed provide some break on long-term spending, but there has to be a better way.”

Darrell Duffie, a professor at Stanford, wrote: “This is a second chance to gridlock. A budget passed by Congress already authorizes the necessary funding.”

Regardless of the position of economists, congressional Republicans have shown no signs of backing down over a debt-limit confrontation.

But one influential outside conservative group is suggesting that the debt-limit battle may not be the best option in the fight to restrain spending.

Tim Phillips, president of Americans for Prosperity, a conservative group partially backed by the billionaire Koch brothers, said in an interview that he saw other looming debates as better battlegrounds.

These include a series of sharp spending cuts set to take effect in early March and a need to pass a resolution funding the government for the next year in late March.

“The number 1 threat to long-term American prosperity is government overspending,” Phillips said. “You don’t get at that as well through a debt-limit fight.”

He said Republicans should fight to preserve the automatic spending cuts, known as the sequester, and be ready to demand deep cuts to keep the government running past March.

“Those are near-term enforceable cuts,” he said. “Those are leaner and better fights to actually cut back government spending.”

By contrast, he said, a deal over the debt limit is likely to provide only illusory cuts.

“An overemphasis on the debt limit also provides more leeway for the left to try to get ‘X’ number of tax increases to go along with the debt limit,” he said. “The tax increases kick in immediately and the spending cuts don’t.”