* Strong data raises questions on Fed stimulus timing
* Smithfield shares soar, China's Shuanghui to buy
* SLM Corp jumps on plan to split into two companies
* Indexes down: Dow 0.6 pct, S&P 0.6 pct, Nasdaq 0.5 pct
NEW YORK, May 29 (Reuters) - U.S. stocks fell from record levels on Wednesday as investors continued to question the longevity of the Federal Reserve's stimulus program.
Supportive monetary policies from central banks around the world have lifted equity markets this year, with the S&P 500 up almost 16 percent. On Tuesday, stocks soared and the Dow closed at a record high after the Bank of Japan and European Central Bank reassured investors that policies designed to boost economic growth would stay in place.
Last week, indexes fell on concerns that the program may be scaled back sooner than expected, and strong economic data on Tuesday stirred speculation that the Fed may begin tapering off its program soon. The concerns sent U.S. Treasury debt yields to their highest levels in over a year and pulled equities back from session highs.
"(Tuesday) was the first time we saw rates spike on concerns about the Fed tapering, and if that spreads, it will have negative ramifications for the rest of the market," said Adam Sarhan, chief executive of Sarhan Capital in New York.
While strong corporate earnings have also contributed to the equity market's surge in 2013, central bank stimulus has pushed investors to add to positions on market declines, limiting extended selloffs. Any change to the stimulus program may prompt a round of profit taking.
"There's still a question about how much we can grow without stimulus, and what will happen to the market when rates go up," Sarhan said.
The Dow Jones industrial average was down 96.15 points, or 0.62 percent, at 15,313.24. The Standard & Poor's 500 Index was down 10.24 points, or 0.62 percent, at 1,649.82. The Nasdaq Composite Index was down 18.15 points, or 0.52 percent, at 3,470.74.
The benchmark 10-year U.S. Treasury note was up 2/32, with the yield at 2.1599 percent.
Cyclical companies, closely tied to the pace of economic growth, have been volatile on uncertainty over the Fed's stimulus measures. U.S. Steel Corp fell 1.6 percent to $12.20 and Cliffs Natural Resources lost 2.4 percent to $19.60.
In company news, Smithfield Foods surged 24 percent to $32.30 after China's Shuanghui Group agreed to buy the company for $34 a share.
SLM Corp jumped 11 percent to $25.51 as the S&P's biggest percentage gainer after the student loan provider said it would split the company into two publicly traded entities and named John Remondi its chief executive officer.
Trina Solar Ltd slumped 9.6 percent to $6.19 after the company reported its seventh straight quarterly loss.
Apple Inc Chief Executive Tim Cook said late Wednesday he expected the tech giant to release "several more game changers," hinting that wearable computers could be among them. Shares edged 0.6 percent higher to $444.20.