* China hikes interest rates, threat seen to global growth
* Nasdaq OMX rebalances Nasdaq 100, Apple shares fall
* ISM services sector data for March on tap
* Futures down: Dow 24 pts, S&P 5 pts, Nasdaq 16 pts (Updates prices, adds Pringles deal)
By Rodrigo Campos
NEW YORK, April 5 (Reuters) - U.S. stocks were set to fall at the open on Tuesday after China, a main source of global growth, raised interest rates, while Apple shares fell after the stock's weighting in a widely followed index was cut.
China's central bank increased interest rates for the fourth time since October, raising suspicions that data next week may show inflation rose more than expected in March. Any move to curb overheating in China's economy is seen as negative for global growth.
Also clouding the outlook for the global economy, Portugal's credit rating was downgraded again on Tuesday. The country's biggest banks threatened to stop buying government debt, according to a local news report..
Stock index futures were dragged lower by "China raising its interest rates and a spike in concern over European weakness," said Oliver Pursche, president at Gary Goldberg Financial Services in Suffern, New York.
Apple Inc had its weighting cut in a rebalancing of shares in the Nasdaq 100, forcing some to sell the iPhone maker's stock. Once the rebalancing is effective on May 2, the projected weight of Apple will be 12.33 percent of the index compared with its current 20.49 percent, Nasdaq OMX said on its website.
The rebalancing requires sponsors of exchange traded funds which track the index, like the heavily traded PowerShares QQQ Trust, to lower their holdings of Apple. Apple fell 1.2 percent in premarket trading.
"In the short-term this is going to have a significant impact and create additional volatility," Pursche said, but "we don't see it as long-term disruptive to the growth and performance of the individual securities."
Shares of Microsoft Corp, whose weighting will rise, gained 1.4 percent before the open.
S&P 500 futures fell 5 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration of the contract. Dow Jones industrial average futures lost 24 points and Nasdaq 100 futures dropped 16 points.
Other tech stocks in focus include Texas Instruments after it launched a $6.5 billion takeover bid for National Semiconductor Corp, offering a 78 percent premium. National Semi traded up 71.6 percent at $24.15 premarket.
Procter & Gamble Co said it will sell its Pringles potato chips business to Diamond Foods Inc for $1.5 billion in stock, sending Diamond shares up 9.3 percent at $62.51 before the open.
Investors will scour the minutes from the latest meeting of the Federal Reserve's policy-setting committee. Fed Chairman Ben Bernanke said a recent rise in U.S. inflation was driven primarily by global commodity prices and was unlikely to persist.
Economic news includes the release of the Institute for Supply Management's March services sector index at 10 a.m. (1400 GMT). Economists in a Reuters survey forecast the index slipping to 59.5 from 59.7 in February.
The S&P 500 faces strong technical resistance after closing just shy of 1,333 for a second straight session on Monday, a level it has not been able to breach at the close since mid-February.
The level marks a doubling of the 12-year low hit in March 2009 and is not far from 1,344, the S&P's 2011 high and its highest since June 2008.
About 5.94 billion shares traded on the New York Stock Exchange, NYSE Amex and Nasdaq, the lowest total so far this year. (Reporting by Rodrigo Campos; Editing by Kenneth Barry)