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* Dow up 0.32 pct, S&P up 0.04 pct, Nasdaq down 0.88 pct
* "Quadruple witching" leads to volatility say traders
* Defensive stocks lead; tech and communication services lag
* Nike jumps after results top estimates, boosts S&P and Dow
* Fed's Williams says central bank open to reassessing views (Adds details, updates prices)
By Medha Singh
Dec 21 (Reuters) - Wall Street swung between losses and gains in volatile trading on Friday that traders blamed on the expiration of stock futures and options, with only the defensive sectors staying higher consistently, highlighting concerns over slowing growth.
The S&P 500 was up much as 1.5 percent at its highest, before falling 0.36 percent to a session low. The S&P and Dow Industrials though stayed higher for most of the session, while the Nasdaq, which came within a whisker of confirming bear market territory on Thursday, was largely lower.
The volatility was mainly due to "quadruple-witching" — when options on stocks and indexes as well as futures on indexes and single-stocks for the quarter all expire — which tends to raise volatility and trading volumes as investors replace expiring positions.
"We had a bit of a bounce, but it's options expiration, so I don't expect the market to regain any substantial strength from the recent selloff," said Peter Cardillo, chief market economist at Spartan Capital Securities in New York.
"Volatility is probably going to be accompanying the movements in the market today."
The markets opened higher and hit session highs after New York Federal Reserve President John Williams said the central bank is open to reassessing its views and listening to market signals that the economy could fall short of expectations. However, he said that for now further rate hikes appear appropriate.
Williams' comments on CNBC come after the Fed said on Wednesday it would largely stick to its plan to keep raising interest rates, spooking investors already grappling with mounting evidence of slowing growth and triggering a two-day slide on Wall Street.
Helping stanch the bleeding on Friday was Nike Inc, which jumped 7.85 percent after the company's quarterly results beat Wall Street estimates on strength in North America. The stock was the biggest driver of gains on the Dow Industrials and S&P 500.
The four top gainers among the 11 major S&P sectors included the defensive consumer staples, utilities and real estate indexes.
Most of the markets gyrations came as the technology index and the communication services index, which house high-growth names such as Facebook Inc and Alphabet Inc, swung between gains and losses.
At 11:45 a.m. ET, the Dow Jones Industrial Average was up 72.11 points, or 0.32 percent, at 22,931.71, the S&P 500 was up 0.88 points, or 0.04 percent, at 2,468.30 and the Nasdaq Composite was down 57.66 points, or 0.88 percent, at 6,470.75.
Adding to the nerves was the turmoil in Washington.
President Donald Trump threatened a "very long" government shutdown just hours ahead of a midnight deadline on a funding deal, while the resignation of U.S. Defense Secretary Jim Mattis after falling out with Trump also sparked concerns.
"A big problem is this chaotic administration. There is so much turmoil. It's an ongoing political problem that creates uncertainties," Cardillo said.
"Any rallies are not sustainable until we have capitulation, and so far we haven't had that."
The three main Wall Street indexes are already in correction territory, having fallen more than 10 percent from their record closing highs, and are closing in on bear market territory, which is marked when an index closes more than 20 percent below its closing high.
Declining issues outnumbered advancers for a 1-to-1 ratio on the NYSE and a 1.51-to-1 ratio on the Nasdaq. The S&P index recorded no new 52-week highs and 61 new lows, while the Nasdaq recorded four new highs and 445 new lows.
Reporting by Medha Singh in Bengaluru; Editing by Shounak Dasgupta