Fed uncertainty sends the Dow, S&P 500 down for fifth day NEW YORK (Reuters) - U.S. stocks fell on Thursday, with the Dow and S&P 500 dropping for a fifth straight session after a round of mixed economic data left traders guessing as to when the Federal Reserve would begin to slow its stimulus program. The Dow and the S&P 500 are in their worst stretch since September. However, the moves have been slight, with the S&P 500 down about 1.2 percent over the period. Gross domestic product grew at an annualized rate of 3.6 percent in the third quarter, the fastest pace since the first quarter of 2012 and faster than the 3 percent rate that had been expected. Another report showed that the number of Americans filing new claims for unemployment benefits unexpectedly fell last week in a hopeful sign for the labor market - a day ahead of the November nonfarm payrolls report. Traders have been trying to second-guess how the Fed views strong data and whether the numbers are strong enough for the central bank to slow its $85 billion-a-month bond-buying program, which it said it would do when certain economic metrics meet its targets. "The growing perception that the Fed will taper sooner rather than later may create some anxious moments in the market, as well as some anxiety for investors," said Clark Yingst, chief market analyst at Joseph Gunnar & Co in New York. However, we think this is bullish for stocks and that the decline is a buying opportunity. Expectations that the Fed might start tapering this month were dampened after Dennis Lockhart, the president of the Federal Reserve Bank of Atlanta, said the GDP data "doesn't make a trend and ... doesn't drive me to the conclusion that we've had a breakout in terms of growth." The Dow Jones industrial average .DJI slipped 68.26 points, or 0.43 percent, to end at 15,821.51. The Standard & Poor's 500 Index .SPX fell 7.78 points, or 0.43 percent, to finish at 1,785.04. The Nasdaq Composite Index .IXIC dropped 4.84 points, or 0.12 percent, to close at 4,033.17. The Dow and the S&P 500 are on track to post their first negative week in nine. Wall Street's recent rally, which took the Dow and the S&P 500 to all-time highs, came mostly on expectations that the Fed would hold steady with its stimulus. The three major U.S. stock indexes have each climbed more than 20 percent this year. Apple (AAPL.O) rose 0.5 percent to $567.90 after China Mobile Ltd (0941.HK), the country's largest mobile operator, said it was still negotiating to offer iPhones on its network. A media report had earlier said that the long-awaited agreement had been reached. Earlier, Apple hit a 52-week high just above $575. But Microsoft (MSFT.O) fell 2.4 percent to $38 in heavy volume. It was the biggest points decliner by far in the Nasdaq 100 .NDX and outweighed Apple's boost. J.C. Penney Co Inc (JCP.N) shares tumbled 8.4 percent to $8.85 after Morgan Stanley reiterated its "underweight" rating on the stock and said November's 10 percent sales growth was not enough to change the company's outlook. Other major U.S. retailers posted disappointing sales for November as cautious shoppers pinched their pennies at the start of the holiday season. Costco (COST.O) shares fell 1.6 percent to $120.95 after the warehouse club chain said sales at stores open at least a year rose 2 percent, below the 3.3 percent increase that analysts were expecting. But the stock of Dollar General Corp (DG.N) jumped 6.1 percent to $59.81 and ranked as the S&P 500's best performer after the discount retailer posted third-quarter earnings and said same-store sales rose 4.4 percent in the same period. About 64 percent of the stocks traded on the New York Stock Exchange closed lower for the day, while 52 percent of Nasdaq-listed shares ended in negative territory. About 5.1 billion shares traded on all U.S. platforms, according to BATS exchange data.