WASHINGTON — The U.S. economy expanded at a 2.8 percent annual rate from July through September, a surprising sign of strength ahead of the 16-day partial government shutdown. Exports rose, businesses stocked up, home construction increased and state and local governments spent at the fastest pace in four years.

The Commerce Department says growth increased from a 2.5 percent annual rate in the April-June period to the fastest pace in a year.

Consumers stepped up spending on goods. But overall spending weakened from the second quarter because service spending was essentially flat, in part because of a cooler summer that lowered utility spending.

The third-quarter outcome was nearly a full percentage point stronger than most economists had predicted. Analysts expect the shutdown will slow growth in the October-December quarter.

Many economists expect growth to pick up in 2014, perhaps to as much as 3 percent. The economy should benefit from no additional tax hikes next year, though federal spending is expected to be tightened further. Housing should remain strong and businesses are likely to invest more in new equipment, said Sung Won Sohn, an economics professor at the Martin Smith School of Business at California State University.

“Businesses really need to raise productivity and the best way to do that is by employing new technology,” Sohn said.

Zandi predicts growth of 3 percent in 2014, which would be the best rate in nine years. But that depends largely on Washington policymakers reaching a deal on the budget, no small feat given the increased partisanship that led to last month’s shutdown.