US STOCKS-Wall St to open lower on rate uncertainty

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By Ellis Mnyandu

NEW YORK, Aug 30 (Reuters) - U.S. stocks headed for a lower open on Thursday due to uncertainty about when the Federal Reserve would cut interest rates and as mixed reports on the economy spurred caution.

Government data showed that economic growth held up in the second quarter despite turmoil from the housing sector, helping stock futures trim some losses before the bell.

But investors remained cautious as another report showed that the number of Americans filing for unemployment benefits unexpectedly rose in the latest week, sparking doubts about the labor market's strength.

Given the market uncertainty, investors are likely to be cautious before a speech to be delivered by Fed Chairman Ben Bernanke on Friday.

"The market will probably go into a freeze waiting for the Bernanke speech tomorrow," said Jim Awad, chairman of W.P. Stewart Asset Management in New York.

S&P 500 futures SPc1 fell 8.7 points, below fair value, a formula to evaluate pricing taking into account interest rates, dividends and time to expiration on the contract.

Dow Jones industrial average futures DJc1 shed 66 points, and Nasdaq 100 NDc1 futures fell 6 points.

Bernanke will address a meeting of central bankers, and Wall Street will be looking for evidence the Fed is any closer to cutting interest rates.

On Wednesday a letter in which Bernanke said the central bank was "prepared to act as needed" to ensure credit market troubles did not harm the economy sparked a rally in stocks, but on Thursday an article by Wall Street Journal Fed correspondent Greg Ip said the Fed was in no rush to cut interest rates, curbing investor optimism.