WASHINGTON  Fear that the financial crisis is infecting once-healthy economies created another white-knuckle day for investors Friday, causing stocks to tumble from Tokyo to New York.

Uncertainty also roiled currency markets as investors continued to turn to the security of the United States dollar and the Japanese yen and drove down currencies of developing countries like Brazil, Ukraine and South Korea and even of developed countries like Britain.

In the United States, where the crisis began, investors were less alarmed than elsewhere. A rout in Asian and European stock markets sent the Dow Jones industrial average swooning by more than 500 points in early trading in New York, but trading recovered enough ground through the day to leave the Dow down 312.30 points, or 3.6 percent.

Just a year ago, a drop of that size would have been considered a black day in the markets, but in these days of routine triple-digit declines, it offered a modicum of relief to traumatized investors.