The long-feared capitulation of American consumers has arrived. According to Thursday’s G.D.P. report, real consumer spending fell at an annual rate of 3.1 percent in the third quarter; real spending on durable goods (stuff like cars and TVs) fell at an annual rate of 14 percent.

To appreciate the significance of these numbers, you need to know that American consumers almost never cut spending. Consumer demand kept rising right through the 2001 recession; the last time it fell even for a single quarter was in 1991, and there hasn’t been a decline this steep since 1980, when the economy was suffering from a severe recession combined with double-digit inflation.

Also, these numbers are from the third quarter — the months of July, August, and September. So these data are basically telling us what happened before confidence collapsed after the fall of Lehman Brothers in mid-September, not to mention before the Dow plunged below 10,000. Nor do the data show the full effects of the sharp cutback in the availability of consumer credit, which is still under way.

So this looks like the beginning of a very big change in consumer behavior. And it couldn’t have come at a worse time.

It’s true that American consumers have long been living beyond their means. In the mid-1980s Americans saved about 10 percent of their income. Lately, however, the savings rate has generally been below 2 percent — sometimes it has even been negative — and consumer debt has risen to 98 percent of G.D.P., twice its level a quarter-century ago.

Some economists told us not to worry because Americans were offsetting their growing debt with the ever-rising values of their homes and stock portfolios. Somehow, though, we’re not hearing that argument much lately.