* Dow Jones industrial average breaks six-week streak of gains
* JC Penney's stock is S&P 500's biggest percentage decliner
* Priceline gains on results, near $1,000 a share
* BlackBerry open to going private, sources tell Reuters
* Dow down 0.5 pct, S&P 500 off 0.4 pct, Nasdaq off 0.3 pct
By Caroline Valetkevitch
NEW YORK, Aug 9 (Reuters) - U.S. stocks fell on Friday and posted their biggest weekly decline since June as investors focused on when the Federal Reserve would begin to scale back its stimulus.
All but one of the 10 S&P 500 sector indexes ended lower.
The stock of J.C. Penney Co. skidded 5.8 percent to $12.87 and ranked as the S&P 500's biggest percentage decliner. Bill Ackman, the company's top investor, urged the retailer's board on Friday to replace its chairman.
Richard Fisher, president of the Federal Reserve Bank of Dallas, reiterated late Thursday that the central bank will probably begin cutting back on its massive bond-buying stimulus next month, as long as economic data continues to improve.
The lack of clarity over the Fed's plans gave investors reason to pull a record $3.27 billion out of U.S.-based funds that hold Treasuries in the latest week ended Aug. 7, data from Thomson Reuters' Lipper service showed on Thursday.
"People are looking ahead to the September FOMC meeting and the prospect that the Fed begins its long-awaited exit strategy," said Michael Sheldon, chief market strategist at RDM Financial, in Westport, Connecticut.
The Dow Jones industrial average dropped 72.81 points, or 0.47 percent, to end at 15,425.51. The Standard & Poor's 500 Index declined 6.06 points, or 0.36 percent, to 1,691.42. The Nasdaq Composite Index fell 9.02 points, or 0.25 percent, to close at 3,660.11.
For the week, stocks posted their biggest declines since mid-June. The Dow fell 1.5 percent, snapping a six-week string of gains. The S&P 500 dropped 1.1 percent for the week and the Nasdaq slid 0.8 percent.
A week ago, both the Dow and the S&P 500 ended at record closing highs.
Stocks extended losses late in the session. President Barack Obama said he will make a decision on the nomination for the Federal Reserve chairman in the fall. Fed Chairman Bernanke is expected to step down when his second four-year term ends on Jan. 31.
Bernanke rattled markets in late May by saying the Fed would begin to ease back on its stimulus program once the economy shows some improvement.
While many investors are concerned that economic growth will stall without the Fed's help, stock prices have been supported by some strong earnings and encouraging data overseas.
The S&P 500 is up 18.6 percent for the year so far.
In China, industrial output rose more than expected, adding to a string of data that indicated the economy may be stabilizing after an extended period of tepid growth.
U.S. economic data showed wholesale inventories unexpectedly fell 0.2 percent in June, marking a second straight month of declines, versus expectations calling for a gain of 0.4 percent.
U.S.-listed shares of BlackBerry Ltd jumped 5.7 percent to $9.76 after Reuters reported that the Canadian smartphone maker was warming to the idea of going private, citing sources familiar with the situation.
Priceline.com Inc, rose 3.9 percent to $969.89 a day after the online travel company reported earnings that beat expectations and gave a strong outlook. Some analysts speculate the stock's price will cross $1,000 soon, which would be a first for a Standard & Poor's 500 stock.
Earnings season is winding down, with 446 companies in the S&P 500 having already reported. Of those, 68 percent have exceeded analysts' expectations, slightly above the 67 percent beat rate over the past four quarters, Thomson Reuters data showed.
Volume was roughly 5.3 billion shares traded on the New York Stock Exchange, the Nasdaq and the NYSE MKT, below the average daily closing volume of about 6.36 billion this year.
Decliners slightly outnumbered advancers on the NYSE by a ratio of about 15 to 14. On the Nasdaq, about three stocks fell for every two that rose.