NEW YORK - (AP) - Stocks are plummeting at the close after anxietyovertook investors on the first trading day since Standard & Poor'sdowngraded American debt. The Dow Jones industrials closed down 634 points, or 5.5percent, to 10,809 Monday. It was the first time the Dow fell below11,000 since November and its biggest one-day point drop sinceDecember 2008. The S&P 500 is closing down 79or 6.7 percent, at 1,119.46. TheNasdaq is down 174.72, or 6.9 percent, at 2,357.69. More than 69stocks fell for every one that rose on the New York Stock Exchange.Trading volume was heavy at 9.7 billion shares. Investors are worried about the slowing U.S. economy andescalating debt problems threatening Europe. Money flowed out ofstocks and into safer investments, including Treasurys and gold.