WASHINGTON — The economy picked up speed in the summer, growing at a brisk 3.9% pace, the fastest in 11⁄2 years and an impressive performance even as a credit crunch plunged the housing market deeper into turmoil.

The latest snapshot of the country’s economic health, released by the Commerce Department today, suggested that the economy is demonstrating much resilience and thus far holding up well to the strains in the housing and credit markets, which had intensified during the third quarter and rocked Wall Street.

A second report from the department showed construction spending rose 0.3% in September, the best showing in four months. All-time high spending in both commercial construction by private builders and government projects more than offset weakness in home building.

For the entire July-to-September quarter, individuals ratcheted up their spending. American businesses sold more goods abroad and boosted some investment at home. Those were main factors helping to push up overall economic activity during that period.

The third quarter’s growth rate was up slightly from a 3.8% pace logged in the second quarter. It marked the strongest showing since the first quarter of last year.

The increase in gross domestic product exceeded analysts’ forecasts for a 3.1% growth rate for third quarter. Gross domestic product is the value of all goods and services produced within America and is considered the best barometer of the country’s economic fitness.

The White House was pleased that problems in housing didn’t spread widely through other parts of the economy during the summer as some feared. “This is an extremely resilient economy,” the chairman of President Bush’s Council of Economic Advisers, Ed Lazear, said. “It is really quite remarkable.”

Builders slashed investment in housing projects by 20.1%, on an annualized basis, in the third quarter, the largest drop in a year. That provided stark evidence of the darkening housing picture.

“This may have been the summer of the housing market’s discontent but it clearly wasn’t for the rest of the economy,” Joel Naroff of Naroff Economic Advisors said.

The new figures on the economy come as the Federal Reserve meets for a second day today to weigh whether it needs to lower a key interest rate to protect the economy down the road from the ill effects of the ailing housing market. Wall Street investors are betting on a smaller, one-quarter percentage point cut. That would follow up on a bolder half-percentage point reduction ordered in September, the first rate cut in more than four years.

Stocks were up in trading before the Fed’s decision. The Dow Jones industrials advanced 70 points.