WASHINGTON — A growing fear of economic deflation helped take the air out of the stock market Wednesday, and another white-knuckle final hour on Wall Street pushed the Dow Jones industrials under 8,000 to their lowest close since the financial meltdown began.

Consumer prices in October took their biggest monthly plunge in the six decades that records have been kept — a reprieve for shoppers but a danger sign for the economy because falling prices can make a mild recession spiral into something worse.

The drop illustrated once again how quickly the economic danger can shift in tumultuous times like these. The inflation fears that gripped the nation just a few months ago now seem like a distant memory.

"Consumer price inflation has suddenly screeched into reverse," said Brian Bethune, economist at IHS Global Insight. "The inflation threat has disappeared from the radar screen."

Worried about the economic data, a gloomy outlook from the Federal Reserve and the fate of the Big Three automakers, investors yanked money out of the stock market. The Dow drifted lower for most of the day, then plummeted in a tumultuous final hour of trading.

It crossed under 8,000 in the last minutes before the closing bell and closed down 427 points, or about 5 percent, at 7,997 — its lowest close since March 2003. The average has dipped below 8,000 on other days since the meltdown began in mid-September but had not closed there.

S&P drops 6 percent

The Standard & Poor's 500, a broader snapshot of the stock market, slipped more than 6 percent. The financial crisis has already wiped out $6.7 trillion of value from the S&P 500 since its October 2007 high. In the same period, the Dow has lost more than 6,000 points.

"I don't know what the catalyst is going to be where we turn the corner and people start buying stocks wholeheartedly again," said Jon Biele, head of capital markets at Cowen & Co. "People got out of the way. The financial situation hasn't changed."