NEW YORK - U.S. stock index futures pointed to a lower open on Tuesday as ongoing concerns over the strength of an economic recovery looked set to eclipse a report expected to show U.S. manufacturing expanded in August.

Some investors say the the global rally in stocks, which has pushed the S&P 500 index up about 50 percent since early March, has run too far ahead of the recovery and may be due for a pullback. Recent falls in China's stock market have added to worries.

The Institute for Supply Management's survey follows similar reports in China and Europe that showed manufacturing around the world continues to stabilize. Stocks rose in Asia overnight but headed lower by as much as 1 percent in Europe.

As investors look for signs the nascent housing recovery is gathering steam, data is also expected to show U.S. pending home sales probably rose 2.0 percent in July, a slowing from June's 3.6 percent.

There are concerns mounting that the market has got ahead of itself, and as investors look to China it appears that they are running into a bout of concern regarding their own economy, said Andre Bakhos, president of Princeton Financial Group in Princeton, New Jersey.

Looking ahead to the data releases, he said: The market has to be certain there is no economic weakness, especially with the concerns in China - that would totally pull the rug from under the market.

S&P 500 futures SPc1 fell 5.0 points and were below 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 DJc1 lost 52 points and Nasdaq 100 futures NDc1 dropped 6.25 points.

The ISM's manufacturing index, due at 10 a.m. (1400 GMT) along with the housing data, will likely show a reading of 50.5, up from 48.9 in July, according to forecasts of the 78 economists polled by Reuters. That would be the first positive reading since just after the recession began. A reading below 50 points to contraction while a reading above 50 points to expansion.

Following a familiar pattern, financials and commodity-related stocks sold off before the market opened. Freeport-McMoRan Copper & Gold Inc lost 0.4 percent while Citigroup Inc fell 2.8 percent. These so-called earlier cyclical stocks are sensitive to fears of economic weakness.

Bank of America Corp is offering to repay part of the U.S. government bailout money, starting with the $20 billion it received in January to help with the acquisition of Merrill Lynch & Co, the Wall Street Journal reported on its website late on Monday. But the shares fell 0.4 percent before the bell.

Shares of on-line auction and services company eBay Inc rose 1.8 percent to $22.54 after the New York Times said eBay will sell its online telephony unit Skype to a group of private investors. (Reporting by Edward Krudy; Editing by Padraic Cassidy)