US STOCKS-Futures retreat, on track to end week sharply lower

By Ryan Vlastelica

NEW YORK, Oct 10 (Reuters) - U.S. stock index futures were lower on Friday, suggesting major indexes could be on track for one of their worst weeks in years, as Thursday's decline on global growth concerns looked likely to be extended.

* The S&P 500 posted its biggest one-day slide in six months Thursday on concerns over the strength of the world economy and its potential impact on corporate earnings. The benchmark index fell below its 150-day moving average for the first time since November 2012, a sign near-tem trends are weaker.

* The selloff was spurred by weak data from Germany, Europe's largest economy, as well as comments from a Fed official who suggested investors had unrealistic expectations about the Fed's eventual rate increase.

* Recent strength in the dollar - which is down 1.1 percent this week but is coming off a 12-week rally - has contributed to concerns about earnings for multinational companies, though some early results, including from Alcoa Inc (NYSE: AA - news) and PepsiCo Inc (NYSE: PEP - news) , were stronger than expected.

* Energy shares will remain in focus as crude oil fell 1.4 percent to $84.54 per barrel, dropping to its lowest level since November 2012. The energy sector has been among the hardest hit in the recent market decline, falling 3.7 percent on Thursday. It is off almost 16 percent from a recent high in June.

* Equities have been volatile of late; the S&P has posted a move of 1 percent in four of the past five sessions. Over the past 14 trading days, the S&P moved an average of 24.86 points from its high to its low, more than twice the 10.35 point average at the start of September.

* Despite a massive rally Wednesday, indexes remain sharply lower for the week. Based on Thursday's close, the Dow is down 2.1 percent this week, the S&P is down 2 percent and the Nasdaq is down 2.2 percent. If the decline implied by futures lasts through the trading day, the S&P may extend its weekly decline to its worst weekly performance since June 2012.

* The CBOE Volatility index is up almost 30 percent thus far this week, and closed Thursday at its highest since early February.

Futures snapshot at 0650 EDT:

* S&P 500 e-minis were down 9.75 points, or 0.51 percent, with 267,406 contracts changing hands.

* Nasdaq 100 e-minis were down 37.75 points, or 0.95 percent, in volume of 49,885 contracts.

* Dow e-minis were down 89 points, or 0.54 percent, with 43,842 contracts changing hands. (Editing by Bernadette Baum)