Dec. 1 (Bloomberg) -- The U.S. economy entered a recession a year ago this month, the panel that dates American business cycles said today, making this contraction already the longest since 1982.

The declaration was made by a committee of the National Bureau of Economic Research, a private, nonprofit group of economists based in Cambridge, Massachusetts. The last time the U.S. was in a recession was from March through November 2001, according to NBER.

Federal Reserve Chairman Ben S. Bernanke today said the economy “will probably remain weak for a time” and the Fed may use unconventional methods, such as buying Treasury securities, to spur growth. Should the recession persist for another five months, consistent with Fed and private forecasts, it would become the longest since the Great Depression.

“It is clearly not going to end in a few months,” Jeffrey Frankel, a member of the NBER committee and a professor at Harvard University, said in an interview. “We would be lucky to get done with it in the middle of next year.”

Separate reports today showed the recession has deepened. U.S. manufacturing contracted in November at the fastest rate in 26 years, according to the Institute for Supply Management, based in Tempe, Arizona. The Commerce Department said construction spending fell more than forecast in October as a slump in homebuilding spread to non-residential projects.

Stocks Slump

Stocks worldwide tumbled and yields on U.S. Treasury securities fell to the lowest ever on concern a lack of financing will stunt consumer and business spending.

The NBER designation means the U.S. was the first country to have slipped into a contraction. While definitions differ, the economies of both the euro area and Japan fell into a slump in the second quarter of this year, making it the first simultaneous recession in the three regions in the postwar era.

The loss of 1.2 million jobs so far this year was the biggest factor in determining the starting point of the U.S. recession, the NBER said. By that measure, the contraction probably deepened last month.

Payroll employment probably fell by 325,000 in November, the most since the last recession, according to the median forecast of economists surveyed by Bloomberg News ahead of a Labor Department report due Dec. 5. The jobless rate is projected to increase to 6.8 percent, the highest level since 1993.

Payrolls Drop

U.S. employers cut 240,000 jobs in October, a 10th consecutive decline. The unemployment rate rose to 6.5 percent, the highest level in 14 years, according to Labor Department statistics.

At 12 months, the current contraction is already the longest since the 16-month slump that ended in November 1982, and exceeds the postwar average of 10 months.

The contraction is the second under President George W. Bush’s watch, making him the first U.S. leader since Richard Nixon to preside over two recessions.

“The most important things we can do for the economy right now are to return the financial and credit markets to normal, and to continue to make progress in housing, and that’s where we’ll continue to focus,” White House Deputy Press Secretary Tony Fratto, said in an e-mailed statement. “Addressing these areas will do the most right now to return the economy to growth and job creation.”

Summers, More Action

Lawrence Summers, President-elect Barack Obama’s pick for White House economic adviser, said the economy is getting worse and requires more legislative action.

“Recent economic evidence suggests that the pace of this downturn is accelerating,” Summers said in a statement. He said Obama wants to enact a recovery package “soon after taking office.”

The likely length of this downturn may cast doubt on economists’ view that the business cycle was moderating in recent decades.

“Everyone had thought long, deep recessions were a thing of the past,” Frankel said. “There was a lot of talk of the new economy.”

Although a recession is conventionally defined as two quarters of successive contraction in gross domestic product, the private committee doesn’t require supporting GDP data to make a recession call. Its members focus on month-to-month changes in the economy.

The NBER committee defines a recession as a “significant” decrease in activity over a sustained period of time. The decline would be visible in gross domestic product, payrolls, industrial production, sales and incomes.

Getting Worse

The U.S. economy shrank at a 0.5 percent pace in the third quarter after expanding 2.8 percent in the previous three months. Economists at Goldman Sachs Group Inc. and Morgan Stanley in New York are among those projecting the economy will contract at a 5 percent pace this quarter.

Members of the committee are Frankel; Stanford University professor Robert Hall; Martin Feldstein of Harvard University; Northwestern University economics professor Robert Gordon; NBER president James Poterba; David Romer of the University of California at Berkeley; and Conference Board economist Victor Zarnowitz.

To contact the reporters on this story: Timothy R. Homan in Washington at thoman1@bloomberg.netSteve Matthews in Atlanta at smatthews@bloomberg.net

Last Updated: December 1, 2008 16:56 EST