WASHINGTON — The economy shifted to a higher gear in the spring, growing at its fastest pace in nearly a year as foreign buyers snapped up American exports and tax rebates spurred shoppers at home.

The Commerce Department reported today that gross domestic product, or GDP, increased at a 3.3% annual rate in the April-June quarter. The revised reading was much better than the government’s initial estimate of a 1.9% pace and exceeded economists’ expectations for a 2.7% growth rate.

The rebound comes after two dismal quarters. The economy actually shrank in the final three months of 2007 and limped into the first quarter at a feeble 0.9% pace. The 3.3% growth in the spring was the best performance since the third quarter of last year, when the economy was chugging along at a brisk 4.8% pace.

Still, the growth pickup is not likely to be seen as a lasting sign that the fragile economy is back on solid ground.

The Federal Reserve Chairman, Ben Bernanke, recently warned the economy will be weak through the rest of this year. A growing number of analysts fear that the country will hit another economic pothole in the fourth quarter, as the bracing impact of the tax rebates disappears. And there are concerns exports could tail off as other countries’ economies slow down.

GDP measures the value of all goods and services produced within America and is the best barometer of the country’s economic health.