* AIG weighs on financials after big loss
* Wal-Mart adds to caution as sales miss estimates
* Pending home sales, jobless claims on tap (Updates prices)
By Ellis Mnyandu
NEW YORK, Aug 7 (Reuters) - U.S. stock index futures fell on Thursday as a big loss from insurer American International Group Inc <AIG.N> heightened concerns about the credit crisis and its impact financial companies and the broader economy.
Adding to investors' disappointment after two days of market gains, Wal-Mart Stores Inc <WMT.N> announced July U.S. same-store sales that fell short of Wall Street's expectations, highlighting the pinch consumers are feeling as they grapple with falling home values and higher gasoline prices.
Shares of AIG, the world's largest insurance company, fell more than 10 percent before the bell, while Wal-Mart, the world's largest retailer, shed more than 3 percent. Both are Dow components.
AIG said late on Wednesday it lost $5.36 billion, its third straight quarterly loss, and blamed soured mortgage-related investments.
"It appears that AIG's results disappointment has dampened enthusiasm about the market's recent gains," said Andre Bakhos, president of Princeton Financial Group in Princeton, New Jersey. "We're seeing the remnants of the credit market mess. AIG could be an excuse for the market to take a short-term respite."
S&P 500 futures <SPc1> fell 5.10 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> shed 66 points and Nasdaq 100 <NDc1> futures declined 2.50 points.
A drag from AIG will increase pressure for the financial sector after the company's European rivals, Aegon <AEGN.AS> and AXA <AXAF.PA>, also disappointed investors with sharply lower earnings, keeping a lid on European equity markets.
AIG also reported a general deterioration in its mainstream insurance businesses, which were hurt in particular by a decline in investment income and losses from its mortgage insurer, United Guaranty Corp. For details, see [
]Shares of AIG shares fell to $26.01.
Wal-Mart reported a 3 percent rise in July sales at U.S. stores open at least a year, but that missed Wall Street estimates, and the company issued a cautious forecast for August. [
]. Its shares declined to $58.85.In economic news, data on pending home sales is due at 10 a.m. (1400 GMT) following the release of weekly jobless claims at 8:30 a.m. (1230 GMT).
Stocks rose on Wednesday, building on the previous day's big gains, as a further drop in oil prices and a reassuring outlook from Cisco Systems <CSCO.O> overshadowed persistent credit concerns. (Editing by Kenneth Barry)