NEW YORK » Stocks plunged in the final hour of trading yesterday, sending the Dow Jones industrial average down 679 points - more than 7 percent - to its lowest level in five years after a major credit ratings agency said it might cut its rating on General Motors Corp.

The declines came on the one-year anniversary of the closing highs of the Dow and the S&P. The Dow has lost 5,585 points, or 39.4 percent, since closing at 14,198 on Oct. 9, 2007. The S&P 500, meanwhile, is off 655 points, or 41.9 percent, since recording its high of 1,565.15.

U.S. stock market paper losses totaled $872 billion yesterday and the value of shares overall has tumbled a stunning $8.33 trillion since last year's high. That's based on preliminary figures measured by the Dow Jones Wilshire 5000 Composite Index, which tracks 5,000 U.S.-based companies' stocks and represents almost all stocks traded in America.

Yesterday's sell-off came as Standard & Poor's Ratings Services put GM and its finance affiliate GMAC LLC under review to see if its rating should be cut. GM has been struggling with weak car sales in North America.

S&P also put Ford Motor Co. on credit watch negative. The ratings agency said that GM and Ford have adequate liquidity now, but that could change in 2009.

GM led the Dow lower, falling $2.15, or 31 percent, to $4.76, while Ford fell 58 cents, or 22 percent, to $2.08.

The Dow ended the day at its lows, finishing down 678.91, or 7.3 percent, at 8,579.19. The blue chips hadn't closed below the 9,000 level since the June 30, 2003.

Broader stock indicators also tumbled. The S&P 500 fell 75.02, or 7.6 percent, to 909.92, while the Nasdaq composite index fell 95.21, or 5.5 percent, to 1,645.12.

The Russell 2000 index of smaller companies fell 47.37, or 8.7 percent, to 499.20.

On the New York Stock Exchange, declining issues came to nearly 3,000, while fewer than 250 advanced.

Libor, the bank lending benchmark, for three-month dollar loans rose to 4.75 percent from 4.52 percent on Wednesday. That signals that banks remain hesitant to make loans for fear they won't be paid back.

The yield on the three-month Treasury bill, which moves opposite its price, fell to 0.51 percent from 0.63 percent late Wednesday. Longer-term debt prices fell, with the yield on the 10-year note rising to 3.79 percent from 3.65 percent late Wednesday.

Energy names were among the biggest decliners as the price of oil fell. Exxon Mobil Corp. fell $9, or 12 percent, to $68, while Chevron Corp. fell $9.10, or 12 percent, to $64.

Light, sweet crude fell $1.81 to settle at $86.62 a barrel on the New York Mercantile Exchange, the lowest closing price since October last year.

The tech sector saw less selling than other parts of the market after IBM Corp. affirmed its forecast.

IBM fell $1.55, or 1.7 percent, to $89. Meanwhile, Intel fell 65 cents, or 4 percent, to $15.60. Microsoft fell 71 cents, or 3.1 percent, to $22.30.