US STOCKS-Wall St flat, quadruple witching may cause volatility
* Bullard says stimulus could wind down from October
* Trading may get volatile due to "quadruple witching"
* Dow off 0.2 pct; S&P off 0.1 pct; Nasdaq up 0.1 pct
NEW YORK, Sept 20 (Reuters) - Wall Street was little changed on Friday, as investors waited to see if speeches by several U.S. Federal Reserve officials would shed light on the Fed's surprise decision to maintain stimulus for now and how much longer the program was likely to continue.
The Nasdaq was supported by shares of Apple Inc, which rose 0.6 percent to $475.40 as the company released the latest version of its iPhone product line.
Trading was choppy as Friday marks the "quadruple witching," when stock index futures, stock index options, stock options and single stock futures all expire on the same day. Trading increases as investors replace or repurchase existing contracts.
In addition, all three major U.S. stock indexes, as well as the FTSE and U.S. index trackers, will rebalance their portfolios to match revisions to index weights. This happens at the close of trading, which could push trading volume higher as transactions jump at the exact close.
"Since the largest of these products which are index futures and options expire on the open, the effect is most pronounced at the open. However, with stock and ETF expirations, as well as index rebalancing, occurring at the close, there can also be significant impact on the close," said Ana Avramovic, derivatives Strategist at Credit Suisse in New York, in a note to clients.
Prior to the open, in an interview on Bloomberg TV, St. Louis Federal Reserve Bank President James Bullard said a wind-down of the Fed's $85-billion monthly bond purchase program from October was possible. On Wednesday, the Fed surprised economists and investors with its decision to delay scaling back stimulus from September.
Bullard's interview remarks come on a day when several senior Federal Reserve officials, including himself, are scheduled to speak.
Apple shares rose as its newest smartphone models hit stores across the world. This includes a simultaneous launch for the first time in the crucial Chinese market. Early on Friday, lines had already formed outside Apple stores in New York and San Francisco.
The Dow Jones industrial average was down 27.19 points, or 0.17 percent, at 15,609.36. The Standard & Poor's 500 Index was down 1.57 points, or 0.09 percent, at 1,720.77. The Nasdaq Composite Index was up 3.90 points, or 0.10 percent, at 3,793.29.
Helped by a rally that took the Dow and the S&P 500 to record highs on Wednesday following the Fed's decision, both indexes are now on track for a third consecutive week of gains.
Bullard will speak on monetary policy to the New York Association for Business Economics at 12:55 p.m. EDT (1655 GMT).
Just ahead of that, Kansas City Federal Reserve Bank President Esther George delivers a speech on the economy to the Shadow Open Market Committee in New York at 12:30 p.m.
Federal Reserve Governor Daniel Tarullo speaks on macroprudential regulation in New Haven, Connecticut at 12:40 p.m. EDT.
Minneapolis Federal Reserve Bank President Narayana Kocherlakota talks at a conference on risk in options prices in New York at 1:45 p.m. EDT.
In Washington, Republicans in the U.S. House of Representatives were expected to vote for a bill to gut President Barack Obama's healthcare law while temporarily funding other government programs, ignoring a warning from the White House that the measure would be vetoed.