U.S. stock index futures were up but eased from earlier highs on Tuesday after crude oil jumped and investors awaited testimony from Federal Reserve Chairman Ben Bernanke.

Bernanke is not expected to cut short the Fed's bond buying program. With much of the market's steep gains over the past several months coming since the Fed announced its $600 billion stimulus program, investors have been concerned about the impact of ending it early.

In his testimony to the Senate Banking Committee, Bernanke is expected to remain cautious about the economy despite recent data pointing to improvement.

Bernanke will say the economy is improving, though slow progress in job creation will allow the Fed to keep being accommodative without risking material core inflation in the short term, said Oliver Pursche, president of Gary Goldberg Financial Services in Suffern, New York.

April U.S. crude futures added nearly 1 percent to $97.81 per barrel. The S&P had its weakest performance since November last week on concerns that high oil prices would hamper economic activity.

Oil has soared due to the political instability in the Middle East. In Libya, forces loyal to leader Muammar Gaddafi massed in the western part of the country, residents said, while the United States moved warships and air forces closer to the North African nation.

S&P 500 futures rose 3 points and were above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures added 25 points and Nasdaq 100 futures rose 6 points.

February ISM manufacturing data will be released at 10 a.m. EST <1500 GMT>, along with January construction spending data. The ISM number is seen rising to 61 from 60.8 in the previous month, while construction spending is expected to show a narrower rate of decline than in the previous month.

In the latest overseas economic data, Chinese manufacturing growth slowed to a six-month low in February, suggesting moves to combat inflation may be working. The data was reassuring in the sense that it will probably take some pressure of food and energy inflation. said Goldberg's Pursche.

Fresh Del Monte Produce Inc reported adjusted fourth-quarter earnings and revenue that missed expectations, AutoZone Inc also reported results early Tuesday, while CenterPoint Energy Inc are set to report quarterly results.

General Mills Inc and Nestle SA are among the leading candidates to buy a 50 percent stake in French yogurt maker Yoplait, Bloomberg reported, citing sources.

Stocks rose for a second straight session Monday after billionaire investor Warren Buffett, chairman of Berkshire Hathaway Inc , said the conglomerate needed to make major acquisitions, a sign stocks may be cheap.

(Editing by Jeffrey Benkoe)