By Herbert Lash

NEW YORK (Reuters) - U.S. stocks slid, the dollar dropped to a 2009 low and government bonds fell further on Friday on worries over rising U.S. debt levels after investors questioned the strength of its AAA credit rating.

The U.S. dollar, on track for its biggest weekly fall in two months, took the brunt of growing worries about the U.S. fiscal outlook after Standard & Poor's on Thursday said it might cut Britain's AAA credit rating because of soaring public debt.

The weak dollar helped push up commodities prices, including oil, gold and copper, and buoyed U.S. stocks as investors bought multinationals and the stocks of natural resource companies in anticipation a weaker dollar would underpin profitability from abroad.

The euro broke above $1.40 (88 pence) and sterling hit a 6 1/2-month peak versus the dollar while U.S. stocks, after rising for most of the session, slid before trading ended -- their fourth straight day of declines.

"The general theme today is clearly broad-based U.S. dollar weakness, largely triggered by mounting concerns over the U.S. government debt AAA rating," said Omer Esiner, senior market analyst at Travelex Global Business Payments in Washington.

A weaker dollar can make U.S. assets more appealing to some investors, and companies with operations abroad benefit when they convert overseas earnings into dollars.

Trading volumes were thin in financial markets ahead of long weekends because of U.S. and British public holidays.

"Investors are coming to a realization that interest rates are heading higher and the dollar is going to be under pressure," said Alan Lancz, president of Alan B. Lancz & Associates Inc, an investment advisory firm based in Toledo, Ohio.