The American consumer is king. That’s evident in the latest news about the economy, which showed that a drop in purchases of everything from flat-panel televisions to clothes to cars is pushing the United States into a potentially deep and prolonged recession.

Last week, the Commerce Department reported that consumer spending fell more in the third quarter than at any time since early 1980, which was at the outset of two painful back-to-back recessions. Real gross domestic product — the sum of all that is produced in the United States — declined in the quarter for the second time in the past year. A further huge drop in October consumption suggests the slump will persist.

The view of many people is that growth has stalled because Americans aren’t spending enough. The latest gambit unleashed last week by Treasury Secretary Henry M. Paulson Jr. and Federal Reserve Chairman Ben S. Bernanke is to use $800 billion to shore up consumer borrowing and get people back into stores and onto car lots.

But solving the economy’s woes may not be as simple as inducing us to return to the malls. The underlying reality is that even when consumers are cutting back, they remain a huge factor in the economy — too huge, perhaps.

Many economists have been calling for a more balanced economy that relies less on personal spending and more on investment in the productive capacity of companies. The challenge for Barack Obama and his newly tapped (if experienced) team will be steering the economy back into the black without returning to a path of unrestrained — and unsustainable — consumption.

For now, however, we might not be able to withstand a pullback by consumers because there’s almost no other source of support for the broad economy. Private investment is the typical fallback when consumers retreat. But investment has contributed only one decent quarterly boost to growth in two and a half years. Companies that were hoarding cash in good times won’t use it until things look up. A survey of corporate financial executives by the University of North Carolina and the American Institute of Certified Public Accountants showed that two out of five are planning investment cuts and half aren’t counting on a rebound until 2010.

Without an investment surge, that leaves only exports and government spending to feed growth. Exports have been a bright spot over the past two years (although imports continue to surpass them), and government outlays have also been increasing. But those two components of GDP combined can’t provide anything like the lift that consumers can give.

That’s because of the dominant role that ordinary purchases of goods and services now play in the economy. From World War II until the late 1980s, consumer spending amounted to roughly 65 percent of GDP, and often considerably less. In the most recent decade, that figure has risen almost to 70 percent. In the third quarter of this year — even with the slump in consumption — such purchases accounted for 70.5 percent of all economic activity. While the recession is real, people are still buying — just not as much.

Dialing It Back

It’s plausible to argue that American consumers account for too great a share of the economy. The difference between 65 percent of GDP and 70 percent may seem small. In fact, it’s significant and helps to explain the troubles facing the economy.

Consider that 5 percent of GDP amounts to about $750 billion. That is roughly what the United States borrows annually overseas to finance its trade deficit. Here’s another way of looking at it: An increase of 5 percentage points of GDP in consumption is roughly equal to the amount that personal savings has declined over the past decade. The lesson is: If we don’t save at home, we have to borrow abroad. Either way, we’re spending more than we have. And unless you’re Bernanke and can print all the money you want, at some point that has to stop.

There is nothing new in this, of course, but the question is when and how to change direction. Obama wants to pull up the economy by elevating the amount of government spending and putting more cash in the hands of the middle class, while Paulson and Bernanke are working to make credit easier for consumers to obtain.