* Oil prices fall after Goldman Sachs cuts forecast
* S&P 500 posts biggest weekly gain since July
* Dow up 0.6 pct, S&P up 0.5 pct, Nasdaq up 0.5 pct (Updates with volume, details on weekly gains)
By Caroline Valetkevitch
Sept 11 (Reuters) - U.S. stocks rose on Friday and the S&P 500 posted its biggest weekly gain since July as investors weighed whether the Federal Reserve will raise interest rates next week.
Energy shares dropped, however, after Goldman Sachs cut its oil price forecast through next year.
Eight of the 10 S&P 500 sectors closed higher, led by gains in utilities, which tend to rise as bond yields fall. The index ended up 0.8 percent, while 10-year U.S. Treasury note yields dipped.
Investors are awaiting next week's Fed monetary policy meeting and news on whether it will raise benchmark U.S. rates for the first time in almost a decade.
"It's really Fed watch. That's what traders are waiting for," said Tim Ghriskey, chief investment officer of Solaris Group in Bedford Hills, New York.
"There's speculation the Fed might hold off, and if they do, I think we'll see stocks rally. But to us, it's not a question of if the Fed raises rates but when. It's going to happen."
The Dow Jones industrial average rose 102.69 points, or 0.63 percent, to 16,433.09, the S&P 500 gained 8.76 points, or 0.45 percent, to 1,961.05 and the Nasdaq Composite added 26.09 points, or 0.54 percent, to 4,822.34.
For the week, the S&P was up 2.1 percent and the Nasdaq rose 3.0 percent, registering their biggest weekly percentage gains since mid-July. The Dow was up 2.1 percent for the week, its best weekly percentage increase since late March.
Stocks have been volatile since China devalued its currency in August amid concerns of sputtering growth in the world's second-largest economy. The S&P 500 has had moves of at least 1 percent in 11 sessions since Aug. 20.
The Fed has said it will raise rates when it sees a sustained economic recovery, especially in the job market.
The day's data signaled moderate economic growth and tame inflation. U.S. consumer sentiment dropped to its lowest in a year in early September, while producer prices for August were flat.
Oil prices fell after the Goldman forecast, which cited oversupply and concerns over China's economy. Goldman said crude could fall as low as $20 a barrel. ConocoPhillips, down 2.2 percent at $47.36, was the biggest drag on the S&P 500.
Gilead rose 2.2 percent to $109.63 after the company's $10 billion debt offering this week fueled speculation it was planning a big acquisition.
On the down side, Zumiez fell 32.5 percent to $14.63 after the sports apparel and accessories maker forecast third-quarter sales and profit below analysts' estimates.
Volume was light. About 6.0 billion shares changed hands on U.S. exchanges, compared with the 8.0 billion daily average for the past 20 trading days, according to Thomson Reuters data.
Advancing issues outnumbered declining ones on the NYSE by 1,629 to 1,429, for a 1.14-to-1 ratio on the upside; on the Nasdaq, 1,565 issues rose and 1,216 fell for a 1.29-to-1 ratio favoring advancers.
The S&P 500 posted one new 52-week high and 10 new lows; the Nasdaq recorded 32 new highs and 87 new lows. (Editing by Nick Zieminski and James Dalgleish)