WASHINGTON — The U.S. economy's vital signs may not confirm a diagnosis of depression. The symptoms increasingly point to one.

As in the Great Depression, world trade is collapsing, wealth is evaporating and the banking system is broken. Deflation is a growing threat as companies slash production, pay and prices. And leaders worldwide are having difficulty making headway in halting the self-perpetuating decline.

"We are tracking 1929-1930," says Barry Eichengreen, a professor of economics and political science at the University of California, Berkeley.

The result: This contraction may leave a lasting imprint on the economy and society, just as the Depression did. In the wake of the devastation of the 1930s, Americans swore off stocks, husbanded their own resources and looked to the government for help. Now, another generation might draw some of the same lessons from the deepest economic collapse of their lifetime.

"This is going to scar the collective psyche," says Mark Zandi, chief economist at Moody's www.Economy.com in West Chester, Pa. "People will become much more conservative in borrowing, lending and investing."

There's no official definition of what qualifies as a depression. In the 1930s, the unemployment rate rose to 25 percent and the economy shrank by more than a quarter.

No economist forecasts a return to the breadlines and shantytowns of that era. "Though the current recession is unquestionably severe, it pales in comparison with what our parents and grandparents experienced in the 1930s," White House chief economist Christina Romer said in a speech last week in Washington.

Still, the economy is getting closer to some of the metrics academics cite as constituting a depression, if not a "great" one.

Economist Robert Barro defines a depression as a 10 percent fall in per-capita gross domestic product and consumption. The Harvard University professor sees roughly a 30 percent chance of that occurring now.

Billionaire Warren Buffett said last week the economy "has fallen off a cliff" and is unlikely to turn around soon. The Berkshire Hathaway Inc. chief executive officer also told the CNBC television network that efforts to stimulate recovery may lead to inflation higher than the 1970s.

The economy contracted at a 6.2 percent annual rate in the last quarter of 2008 and will shrink at a 7 percent rate in the first three months of 2009, projects Jan Hatzius, chief U.S. economist at Goldman Sachs Group Inc. in New York.

Bradford DeLong, a former Treasury official who is now a professor at Berkeley, says a depression is a two-year period with unemployment at 10 percent or above. He says that's possible, though not likely. The jobless rate rose to 8.1 percent in February, a 25-year high.

Some industries are already in a depression, led by housing, where the decline accelerated in recent months as the credit crisis intensified. During the past four years, residential investment is down by 37 percent. That compares with an 80 percent drop in spending on home building from 1929 to 1932.

"The past five months have been among the most difficult in U.S. economic history," Robert Toll, chief executive of Horsham, Pa.-based Toll Brothers Inc., said Feb. 11, after the largest U.S. luxury homebuilder reported a 51 percent sales drop.

In the auto industry, U.S. sales have fallen 55 percent from their July 2005 peak. Production of cars and trucks plunged in January to an annual rate of 3.9 million, the lowest since the Federal Reserve began keeping records in 1967, and 67 percent below the January 2005 level.

Things are so bad that auditors have questioned the ability of General Motors Corp., the biggest U.S. automaker, to continue as a going concern. U.S. motor vehicle output slumped 75 percent from 1929 to 1932, according to statistics in the book "American Automobile Workers 1900-1933," by Joyce Shaw Peterson.

"We are in an automotive depression," said Efraim Levy, an equity analyst for Standard & Poor's in New York.

The financial-services industry has also been decimated. Since the crisis began in the middle of 2007, institutions worldwide have racked up $1.2 trillion in credit losses and writedowns. Announced job cuts have topped 280,000.

"You've had a major disruption of the financial system, just like the 1930s," says Mark Gertler, a New York University professor who collaborated on research about the Depression with Fed Chairman Ben S. Bernanke. In the '30s, more than 10,000 banks went bust.

Lawrence Summers, director of the White House's National Economic Council, has also voiced concern about a return of deflation, which wreaked havoc on the economy in the Great Depression. As wages fell back then, workers had a harder time paying their debts, aggravating the banking industry's woes.