Washington  - US stocks were mixed on Wednesday with gains in high technology and a slower decline in blue chips and general stocks as gridlock continued in Washington over prompt passage of a week-old White House rescue plan for Wall Street.

Federal Reserve chairman Ben Bernanke warned Congress of "grave threats" facing the American economy and financial system, and of the consequences of failure to act.

"The downside risks to the outlook ... remain a significant concern," Bernanke told the Joint Economic Committee of the US Congress.

US President George Bush was preparing to speak to the country late Wednesday (0100 GMT Thursday) in an effort to break the congressional logjam and defuse public opposition to his controversial 700-billion-dollar bailout of bad mortgage debts and related securities.

The announcement that legendary investor Warren Buffett would put 5 billion dollars into Goldman Sachs Group Inc, along with the uncertainty over the rescue plan, caused the Standard & Poor's 500 Index to swing between gains and losses more than 40 times during the day, Bloomberg financial news service reported.

The announcement of Buffet's move came as the investment banking firm was converting itself to a normal bank holding company, a decision reached this week to obtain greater access to loans from the US Federal Reserve. The conversion will place Goldman Sachs under greater government scrutiny.

Buffet's purchase of a stake in Goldman Sachs could be influential in raising additional capital as the investment bank tries to stabilize itself during the ongoing US credit crunch.

The blue chip Dow Jones Industrial Average shed 29 points, or 0.27 per cent, to 10,825.17. The broader Standard & Poor's 500 Index lost 2.35 points, or 0.20 per cent, to 1,185.87. The technology- heavy Nasdaq Composite Index gained 2.35 points, or 0.11 per cent, to 2,155.68.

On Tuesday, the three indices each shed more than 1 per cent. On Monday and through last week, stocks lurched up to 4 per cent a day both ways.

The US currency rose to 68.40 euro cents from 68.09 euro cents on Tuesday. The greenback rose against the Japanese yen to 106.13 from 105.25 yen on Tuesday. (dpa)