* U.S. GDP, jobless claims data beat expectations
* Apple climbs after China Mobile says iPhone talks continue
* J.C. Penney falls on Morgan Stanley note
* Dow down 0.3 pct, S&P 500 off 0.4 pct, Nasdaq down 0.1 pct
NEW YORK, Dec 5 (Reuters) - U.S. stocks declined on Thursday after a round of mixed economic data left traders guessing how soon the Federal Reserve would begin to wind down an asset-purchase program that has helped equities rally this year.
Both the Dow and the S&P 500 were on track for their fifth straight day of losses, the worst stretch for the indexes since September. However, the moves have been slight, with the S&P 500 down about 1.1 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.
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 Atlanta Fed President Dennis Lockhart 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 was down 50.15 points, or 0.32 percent, at 15,839.62. The Standard & Poor's 500 Index was down 6.29 points, or 0.35 percent, at 1,786.52. The Nasdaq Composite Index was down 4.41 points, or 0.11 percent, at 4,033.58.
The Dow and the S&P 500 are on track to post their first negative week in nine.
Stocks' recent rally, which lifted the Dow above 16,000 and the S&P 500 above 1,800, largely came 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 rose 0.9 percent to $569.89 after China Mobile Ltd, 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 fell 2.7 percent to $37.88 in heavy volume. This was the stock's largest daily drop in three months, making it the biggest points decliner by far in the Nasdaq 100 and outweighing Apple's boost.
J.C. Penney Co Inc tumbled 8.7 percent to $8.82 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 shares fell 1.4 percent to $121.26 after he 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 jumped 6.2 percent to $59.85 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.