Blue chips closed slightly lower Thursday, giving up earlier gains as oil prices rose. Trading was moderate before the holiday weekend. The Dow Jones industrial average finished at 10,442.87, down 13.15 points or 0.13 percent. The Nasdaq, helped by stocks such as Yahoo!, rose 0.84 of a point, or 0.04 percent, to close at 1,991.06. (The Internet media company’s board authorized a $3 billion, five-year, stock-buyback program.) Economists remained bullish about an expanding U.S. economy, even as the week saw mixed economic news: New orders for American durable goods showed only slight gains in February, but sales of new homes soared. On the Big Board, IPG closed at $12.01, up 2.6 percent, and Omnicom finished at $87.16, down 0.8 percent. WPP, traded as American Depository Receipts on the Nasdaq, ended 2.9 percent lower at $57.02. U.S. financial markets were closed for Good Friday.