New York ? Wall Street extended its steep decline Friday, propelling the Dow Jones industrials down more than 500 points over two days after investors gave in to mounting concerns that borrowing costs would climb for both companies and homeowners. It was the worst week for the Dow and the Standard & Poor’s 500 index in five years.

Investors cast aside a stronger-than-expected read on the economy and maintained negative sentiment of Thursday, when the market shuddered amid worries over the U.S. mortgage and corporate lending markets. Investors globally took flight from equities, shifting cash into safer investments in Treasurys.

Although the market has often rebounded after a steep drop – even in recent weeks – investors appeared unable Friday to set aside their concerns about a weakening housing market and tightening credit.

Broader stock indicators also fell Friday. The S&P 500 ended down 23.71, or 1.60 percent, to 1,458.95. For the week, the S&P gave up 4.90 percent. The Nasdaq composite index fell 37.10, or 1.43 percent, to 2,562.24. It was down 4.66 percent for the week.

A Commerce Department report that the U.S. gross domestic product rose at a better-than-expected pace in the second quarter appeared to do little to quell investors’ unease. GDP increased at a 3.4 percent annual rate, indicated that the drag from the housing sector lessened. Economists had expected an increase of 3.3 percent.

Although the GDP reading might have reassured investors that the economy was more than holding up even with soaring fuel prices, it could also raise the possibility that the Federal Reserve, ever vigilant about inflation, might put off a rate cut or even raise rates, which would exacerbate the market’s intensifying concerns about credit.

“I think people are really cautious right now. We’re seeing the convergence of a whole host of sort of unrelated or only slightly related issues,” said Randy Frederick, director of derivatives at Charles Schwab & Co. He contends market volatility will remain as investors sort through issues such as the availability of credit for corporate buyouts, soured subprime mortgages and rising energy prices.

The Dow fell 208.10, or 1.54 percent, to 13,265.47. For the week, the index fell more than 585 points, or 4.23 percent.