* Apple drags all three indexes; Alphabet down 2.6 pct
* S&P's healthcare, IT indexes down 0.9 pct
* Indexes down: Dow 0.44 pct, S&P 0.46 pct, Nasdaq 0.87 pct (Updates to early afternoon)
By Yashaswini Swamynathan
June 17 (Reuters) - A drop in Apple dragged down all three major U.S. stock indexes on Friday afternoon even as investors remained wary of global economic growth worries and an impending referendum on Britain's European Union membership.
Britain will vote on June 23, an event that has weaved in uncertainty across the globe, battering stocks and bond yields for the past week and spiking the demand for safe-haven assets such as gold and the yen.
"Risk appetite has declined because of the Brexit vote," said Jeremy Zirin, head of investment strategy at UBS Wealth Management Americas in New York.
"Sectors that are performing well today are only those that have reacted positively to the dollar," he added.
The dollar fell 0.22 percent to 94.35 against a basket of major currencies.
Oil prices jumped 3 percent, snapping a six-day slide and sending the S&P energy sector up 0.64 percent, the only bright spot on the index.
The U.S. Federal Reserve left short-term interest rates unchanged on Wednesday and cut its forecast for economic growth, but stock markets' reaction to the largely expected outcome has been muted.
At 12:40 p.m. ET (1640 GMT), the Dow Jones Industrial Average was down 78.09 points, or 0.44 percent, at 17,655.01.
The S&P 500 was down 9.55 points, or 0.46 percent, at 2,068.44.
The Nasdaq Composite was down 41.94 points, or 0.87 percent, at 4,802.98.
The three indexes are on track to close down more than 1 percent for the week.
Nine of the 10 major S&P sectors were lower, while the information technology and healthcare indexes were both down about 0.92 percent. Apple and Alphabet weighed on the S&P the most.
Apple fell as much as 2.3 percent to $95.35 after reports that regulators in Beijing barred iPhone 6 and 6 Plus as they violated a Chinese rival's patent. Apple told CNBC that the phones were available for sale in China and it was appealing the ruling.
Google's parent Alphabet was down 2.6 percent at $704.48.
Merck fell 2.3 percent while Pfizer was off 1.3 percent.
Oracle rose 2.3 percent to $39.54 after the company reported better-than-expected quarterly revenue. The stock gave the biggest boost to the S&P.
Advancing issues outnumbered decliners on the NYSE by 1,713 to 1,224. On the Nasdaq, 1,501 issues fell and 1,166 advanced.
The S&P 500 index showed 9 new 52-week highs and 2 new lows, while the Nasdaq recorded 25 new highs and 28 new lows. (Reporting by Yashaswini Swamynathan in Bengaluru; Editing by Don Sebastian)