The U.S. economy sped up last summer thanks to as surging exports and stronger consumer spending.

Gross domestic product rose at a seasonally adjusted 3.9% annual rate in the third quarter, the U.S. Commerce Department said today in its first estimate of growth for the July-September period.

The increase represented the strongest growth in quarterly GDP since a 4.8% increase during the first quarter of 2006.

U.S. GDP climbed at a 3.8% pace in the second quarter and 0.6% in the first.

Stronger exports during the summer helped power the economy through the U.S. housing slump and tighter credit conditions. Wall Street economists had expected 3.2% GDP growth during Q3.

Housing, took a big bite out of the U.S. economy in the third quarter. Residential fixed investment dropped by 20.1%, reducing overall GDP by 1.05 percentage points. Second-quarter investment had fallen by 11.8%, taking 0.62 percentage point out of GDP. The 20.1% drop was nearly the worst in the current housing slump; investment in third-quarter 2006 plummeted 20.4%.

Helping drive GDP was its biggest component, consumer spending, which accelerated in the third quarter, rising 3.0% after increasing 1.4% in the second quarter. Purchases of durable goods rose 4.4% in the third quarter, after increasing by 1.7% April through June. Third-quarter non-durables spending rose by 2.7%. Services spending climbed 2.9%. Overall, consumer spending contributed 2.11 percentage points to GDP July through September; it had contributed 1.00 percentage point in the second quarter.

International trade contributed 0.93 percentage point to GDP in the third quarter. U.S. exports surged 16.2% and imports increased 5.2%. In the second quarter, trade added 1.32 percentage points to GDP; exports in that period were 7.5% higher and imports fell by 2.7%.

The price index for personal consumption expenditures rose by 1.7% after increasing 4.3% in the second quarter. But the PCE price gauge excluding food and energy accelerated, rising 1.8% after increasing 1.4% in the second quarter.

Meanwhile, U.S. construction spending unexpectedly climbed in September, with government-financed projects helping builders overcome the housing sector’s deep troubles.

Total spending increased by 0.3% at a seasonally adjusted annual rate of US$1.163 trillion, the U.S. Commerce Department said today. Wall Street had expected September construction spending would decline by 0.4%.

The 0.3% gain marked the first spending increase in four months.