WASHINGTON — The U.S. economy showed surprising growth from July through September, just before the government's partial shutdown. But much of the gain came from a buildup in company stockpiles.

Consumers and businesses slowed their spending — a cautionary sign for the current quarter and early 2014.

Americans did purchase more autos and other long-lasting goods. Yet most analysts say the economy isn't showing enough underlying strength to cause the Federal Reserve to scale back its stimulus any time soon.

Overall, growth accelerated to a 2.8 percent annual rate in the third quarter, the Commerce Department said Thursday. That's up from a 2.5 percent rate in the April-June quarter. And it's nearly a full percentage point higher than economists had predicted.