Stock index futures pointed to a rise of more than 1 percent at the open on Tuesday, but investors remained concerned the rally would not be sustained.

Futures rose after gauges of Chinese and euro zone economic activity came in less gloomy than feared, and the action was a repeat of Monday's futures trade, though Wall Street closed only modestly higher.

Today's gain isn't sustainable. This is exactly what we saw yesterday and the data from overseas wasn't fantastic enough to generate this kind of rise, said Phil Streible, senior market strategist with MF Global in Chicago.

While reads on China's factory sector and German business activity pointed to slowing growth, the slowdown wasn't as harsh as some had feared.

The erosion of Monday's gains were another sign of the volatility that continues to plague markets as investors find few reasons to buy ahead of comments from Federal Reserve Chairman Ben Bernanke at an annual central bank conference in Jackson Hole, Wyoming, on Friday.

Some have speculated Bernanke could unveil fresh measures to revive a struggling U.S. economy, though he is most likely to outline gradual measures, which would disappoint those looking for something as dramatic as a third round of quantitative easing.

The market is putting too much expectation on Jackson Hole, and while Bernanke can say something that would stabilize markets, prospects for (more monetary stimulus) are slim to none, Streible said.

S&P 500 futures rose 9.4 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 149 points and Nasdaq 100 futures rose 18.25 points.

July U.S. new home sales, scheduled for release at 10:00 a.m. <1400 GMT>, will give new insight into the state of the fragile housing sector. Sales are forecast at about 310,000 homes, roughly flat with June.

Banks will continue to be in focus after UBS AG said it plans to slash around 3,500 jobs in a cost-cutting measure. U.S.-listed shares of the lender rose 3.7 percent to $13.68 in premarket trading.

Goldman Sachs Group Chief Executive Lloyd Blankfein hired Reid Weingarten, a high-profile Washington defense attorney, a government source familiar with the matter said late on Monday. Investigations of Goldman and its role in the 2007-2009 financial crisis continue.

Bank of America Corp , one of the most active stocks recently, rose 2 percent to $6.55 in premarket trade.

Omnicare Inc offered to buy smaller rival PharMerica Corp

for $441 million in cash, sending PharMerica shares up 37 percent to $15.01 in premarket. Omnicare rose 9.4 percent to $29.43.

NYSE Euronext said that sporadic issues were affecting delivery in the New York Stock Exchange and NYSE Amex cash equities markets and that repairs were underway.

U.S. stocks ended slightly higher on Monday after four weeks of losses as investors hesitated to take big risks without a catalyst for buying.

(Editing by Padraic Cassidy)