* Central bank policy to remain in focus
* HP rises after comments from CEO
* Celgene up on share repurchase program
* Indexes up: Dow 0.3 pct, S&P 0.3 pct, Nasdaq 0.2 pct
By Leah Schnurr
NEW YORK, June 12 (Reuters) - U.S. stocks were little changed in early trading on Wednesday, gaining modestly amid advances in energy and materials shares, even as investors continued to mull how soon central banks will begin to scale back supportive measures.
Indexes came off their session highs not long after the opening bell on Wall Street.
Hewlett-Packard was the biggest gainer on the blue chip Dow after its chief executive said revenue growth was "still possible" in fiscal 2014. The computer maker was up 4.6 percent at $25.36.
The benchmark S&P 500 had dropped 1 percent Tuesday in volatile trading after Japan's central bank disappointed markets by holding its monetary policy steady.
The lack of further action by the Bank of Japan kindled unease over when the ultra-loose policy put in place by global central banks will be wound down, particularly by the Federal Reserve.
Monetary efforts to boost the economic recovery have been a pillar of the rally in U.S. equities this year, and uncertainty over when the measures will be reined in has prompted investors to unwind trades built around such support.
"We're not getting a lot of direction but volatility has definitely come into play here," said Joe Bell, a senior equity analyst at Schaeffer's Investment Research in Cincinnati.
"There's a bit of uncertainty right now," he said. "It seems like every other week, there's a rumor about when or if this quantitative easing is going to end, how much longer stimulus is going to be in place."
The Dow Jones industrial average gained 38.78 points, or 0.26 percent, to 15,160.80. The Standard & Poor's 500 Index added 4.68 points, or 0.29 percent, to 1,630.81. The Nasdaq Composite Index edged up 5.14 points, or 0.15 percent, at 3,442.09.
The materials sector gained 0.5 percent, while energy shares rose 0.3 percent.
Stocks had begun the session with other asset markets looking stronger, but some of those moves reversed in early trading Wednesday. The dollar eased, while Treasuries prices turned lower after earlier edging up.
Celgene Corp rose 2.1 percent to $121.24 after the company announced an additional $3-billion share repurchase program.
First Solar slipped 3 percent to $50.73, a day after the company reaffirmed its 2013 guidance and announced an 8.5 million share offering.
Cooper Tire & Rubber Co surged more than 40 percent after India's Apollo Tyres Ltd said it would buy the company for about $2.5 billion. Cooper Tire shot up 40.6 percent to $34.52.