In fact, consumers’ income may actually fall more than their spending, so that their attempt to save more backfires  a possibility known as the paradox of thrift.

At this point, however, the instructor hastens to explain that virtue isn’t really vice: in practice, if consumers were to cut back, the Fed would respond by slashing interest rates, which would help the economy avoid recession and lead to a rise in investment. So virtue is virtue after all, unless for some reason the Fed can’t offset the fall in consumer spending.

I’ll bet you can guess what’s coming next.

For the fact is that we are in a liquidity trap right now: Fed policy has lost most of its traction. It’s true that Ben Bernanke hasn’t yet reduced interest rates all the way to zero, as the Japanese did in the 1990s. But it’s hard to believe that cutting the federal funds rate from 1 percent to nothing would have much positive effect on the economy. In particular, the financial crisis has made Fed policy largely irrelevant for much of the private sector: The Fed has been steadily cutting away, yet mortgage rates and the interest rates many businesses pay are higher than they were early this year.

The capitulation of the American consumer, then, is coming at a particularly bad time. But it’s no use whining. What we need is a policy response.

The ongoing efforts to bail out the financial system, even if they work, won’t do more than slightly mitigate the problem. Maybe some consumers will be able to keep their credit cards, but as we’ve seen, Americans were overextended even before banks started cutting them off.

No, what the economy needs now is something to take the place of retrenching consumers. That means a major fiscal stimulus. And this time the stimulus should take the form of actual government spending rather than rebate checks that consumers probably wouldn’t spend.

Let’s hope, then, that Congress gets to work on a package to rescue the economy as soon as the election is behind us. And let’s also hope that the lame-duck Bush administration doesn’t get in the way.