* Indexes have fallen for two straight weeks
* Alcoa to buy RTI International for $1.5 bln
* GM up in premarket, to launch buyback program
* Futures down: Dow 23 pts, S&P 2.75 pts, Nasdaq 3.75 pts (Updates trading, adds Alcoa news)
By Ryan Vlastelica
NEW YORK, March 9 (Reuters) - U.S. stock index futures fell on Monday, continuing a recent downtrend on Wall Street as investors speculated over whether interest rates could be raised sooner than expected.
Major indexes slumped on Friday, with the S&P 500 suffering its biggest one-day loss in about two months, after the U.S. nonfarm payrolls report for February showed jobs growth that was much stronger than expected.
That was seen as possibly pressuring the Federal Reserve to act soon on monetary policy, as the central bank had said it would raise rates when the economy was strong enough to support it.
While a more robust economy is better for stocks in the long run, investors have been concerned that a rate rise too soon - which would raise borrowing costs for companies and individuals - could damp growth as the economy's recovery has been slow.
The S&P 500 has fallen for two straight weeks, but remains about 2 percent from its record closing high. The Dow is also near record levels, while the Nasdaq is 2.4 percent below its record close, which was hit in March 2000.
Premarket volume was light, suggesting investors were reluctant to jump in at current levels. That could amplify market volatility, as could this week's economic data, including retail sales and consumer sentiment, which may provide further insight into the Fed's plans for interest rates.
Alcoa Inc rose 0.5 percent to $14.55 in premarket trading after it said it would buy RTI International Metals Inc for $1.5 billion.
Apple Inc rose 1.1 percent to $128 in premarket trading. The company will be in focus Monday amid its "Spring Forward" event, which will be followed with interest by investors looking for details on its new Apple Watch product.
General Motors said it would launch a $5 billion share buyback and put forward a new plan for capital allocation that promises investors the potential for further cash returns. Shares rose 2.8 percent to $37.55 before the bell.
U.S. shares of BlackBerry fell 4.3 percent to $10.21 in premarket trading after Goldman Sachs downgraded the company to "sell," expecting the smartphone maker's losses to widen in 2016.
Whiting Petroleum Corp rose 3.2 percent to $35.12 before the bell. Late Friday, the Wall Street Journal reported that the company was seeking a possible buyer, though a person familiar with the board's thinking told Reuters he was not aware of any such plan.
CTI BioPharma Corp jumped 24 percent to $3.29 in heavy premarket trading after the company's experimental blood cancer treatment achieved the main goal of a late-stage study.
Futures snapshot at 7:36 a.m. EDT (1136 GMT):
* S&P 500 e-minis were down 2.75 points, or 0.13 percent, with 100,154 contracts changing hands.
* Nasdaq 100 e-minis were down 3.75 points, or 0.09 percent, in volume of 17,606 contracts.
* Dow e-minis were down 23 points, or 0.13 percent, with 14,681 contracts changing hands.
Editing by Bernadette Baum