Dec 17 (Reuters) - Wall Street was mixed on Friday, with the S&P 500 down and Tesla helping keep the Nasdaq in positive territory as investors digested the Federal Reserve"s decision to end its pandemic-era stimulus faster. All three main U.S. stock indexes were set to end with a decline for the week after the Fed on Wednesday signaled three quarter-percentage-point interest rate hikes by the end of 2022 to combat surging inflation. Ten of the 11 major S&P 500 sector indexes fell, with financials (.SPSY) down 1.8%. Other value-oriented sectors including energy (.SPNY), industrials (.SPLRCI) and materials (.SPLRCM) also declined. Real estate (.SPLRCR) rose 0.7%. Tesla (TSLA.O) added 2.2% and Amazon (AMZN.O) gained 1%, helping keep the Nasdaq higher. The S&P 500 growth index (.IGX) dipped 0.1%, while the value index (.IVX) slid 0.7%. Traders also pointed to year-end tax selling and the simultaneous expiration of stock options, stock index futures and index options contracts - known as triple witching - as potential causes for volatility. "It"s a big options expiration day, it will be a significant amount of volume at the close," said Joe Saluzzi, co-manager of trading at Themis Trading in Chatham, New Jersey. "And you"re seeing a lot of short-covering going on in some of those names that have been beaten up a lot." Heavyweight growth stocks including Nvidia (NVDA.O) and Microsoft have outperformed the broader market in 2021, while the Philadelphia SE Semiconductor index (.SOX) has surged 35%. The benchmark S&P 500 index gained 23% in the same period. In afternoon trading, the Dow Jones Industrial Average (.DJI) was down 0.92% at 35,567.3 points, while the S&P 500 (.SPX) lost 0.39% to 4,650.61. The Nasdaq Composite (.IXIC) added 0.38% to 15,238.34. Global stocks also retreated on Friday on concerns about the fast-spreading Omicron variant of the coronavirus, which has impacted trading sentiment since late November. The small-cap Russell 2000 index (.RUT) gained 1.3% after having fallen more than 10% from a record high hit in early November. Oracle (ORCL.N) fell 5.7% after the Wall Street Journal reported the enterprise software maker is in talks to buy electronic medical records company Cerner (CERN.O) in a deal that could be valued at $30 billion. Shares of Cerner surged 14%. read more FedEx Corp (FDX.N) rose 5.3%, boosting the Dow Jones Transport Average Index (.DJT), after the delivery firm reinstated its original fiscal 2022 forecast on Thursday, even as persistent labor woes chipped away profits. read more Declining issues outnumbered advancing ones on the NYSE by a 1.19-to-1 ratio; on Nasdaq, a 1.38-to-1 ratio favored advancers. The S&P 500 posted 21 new 52-week highs and five new lows; the Nasdaq Composite recorded 14 new highs and 309 new lows.