* Fed maintains stimulus measures despite job market improvements
* Merck, MasterCard shares slide after earnings
* U.S. companies hire less, factory growth slows in April
* Dow off 0.7 pct, S&P 500 off 0.6 pct, Nasdaq off 0.7 pct
By Ryan Vlastelica
NEW YORK, May 1 (Reuters) - U.S. stocks fell on Wednesday as the Federal Reserve's decision to stand pat on its current monetary stimulus was not able to offset weak economic figures and several lackluster earnings reports.
The U.S. Federal Reserve stood by its plan to stimulate the economy through bond purchases, and while the central bank noted some improvements in the labor market, it said recent budget tightening in Washington could be a risk to growth.
The statement came in largely as expected. While equities have performed well of late, with the S&P 500 hitting both intraday and closing highs on Tuesday, a trend of discouraging data indicated that the Fed wouldn't ease up on its accommodative monetary policy of quantitative easing.
"That the Fed won't end QE any time soon is positive for stocks in the near term, but the data we've seen is creating a lot of angst for investors," said Mike Gibbs, co-head of the equity advisory group at Raymond James in Memphis, Tennessee.
U.S. private employers added 119,000 jobs in April, well below economists' expectations. A separate report showed the U.S. manufacturing sector expanded only modestly in April.
Adding to concerns, growth in China's factory sector unexpectedly slowed last month as new export orders fell, raising fresh doubts about the world's second-largest economy after a disappointing first quarter.
Materials and energy stocks led declines as expectations of slower growth sent prices of basic materials lower. An index of commodities fell 1.7 percent while the S&P energy index slid 1.1 percent and the S&P materials index lost 1.3 percent. Copper prices fell 3.7 percent, the most in a day since early April 2012.
Exxon Mobil Corp fell 1.1 percent to $88.02 while Freeport-McMoRan Copper & Gold Inc shed 0.8 percent to $30.19.
The S&P 500 has recently ended sessions much stronger than its early lows as traders buy equities on signs of weakness.
"We're a bit overextended, which is leading to some profit taking," said Gibbs, who helps oversee about $400 billion. "But relative to historical measure, we're not in an expensive market, and we would view declines as buying opportunities."
The Dow Jones industrial average fell 98.19 points or 0.66 percent to 14,741.61. The S&P 500 lost 9.97 points or 0.62 percent to 1,587.60. The Nasdaq Composite dropped 21.54 points or 0.65 percent, to 3,307.25.
April marked the S&P 500's sixth consecutive month of gains.
The S&P 500 is up 11.4 percent so far this year.
Disappointing corporate results also weighed on the market. Both MasterCard Inc and Merck & Co posted revenue that fell short of expectations, continuing a trend of prominent companies struggling to grow sales.
MasterCard dropped 2.9 percent to $536.99 while Merck fell 3.1 percent to $45.53 and weighed on the Dow. Visa Inc, a competitor of MasterCard, fell 0.9 percent to $166.89.
Of the 342 companies in the S&P 500 that have reported earnings so far this season, 68.7 percent have beaten expectations and 43.2 percent have reported revenue above forecasts. Over the past four quarters, 67 percent have beaten earnings and 52 percent have beaten revenue expectations.
Shares of wireless carrier T-Mobile US rose 8 percent to $16.53 in its debut on the New York Stock Exchange. The company was created by the merger of MetroPCS Communications and Deutsche Telekom AG's U.S. unit T-Mobile USA.