NEW YORK (Reuters) - The S&P 500 fell for a fourth day on Wednesday, weighed down by disappointing news from Chevron <CVX.N> and Alcoa <AA.N> as earnings season got under way.

Based on the latest available data, the Dow Jones industrial average <.DJI> slid 128.56 points, or 0.95 percent, to end unofficially at 13,344.97. The Standard & Poor's 500 Index <.SPX> slid 8.91 points, or 0.62 percent, to finish unofficially at 1,432.57. The Nasdaq Composite Index <.IXIC> lost 13.24 points, or 0.43 percent, to close unofficially at 3,051.78.

(Reporting by Caroline Valetkevitch; Editing by Jan Paschal)