May 4 (Reuters) - Wall Street's main indexes fell at the open on Monday, as growing investor concern over the conflict in the Middle East dampened the optimism that followed last week's gains.

The Dow Jones Industrial Average fell 82.6 points, or 0.17 percent, to 49,416.66, the S&P 500 opened down 1.7 points, or 0.02 percent, at 7,228.38, and the Nasdaq Composite dropped 2.3 points, or 0.01 percent, to 25,112.18.