WALL STREET STOCKS/AMERICAN EXPRESS <AXP> American Express Co's stock fell sharply, reflecting, in part, investors' disappointment that the company did not make an announcement about its plans for brokerage unit Shearson Lehman Brothers, traders said. The company has said it is studying options for its Shearson unit. Traders said many investors anticipated an announcement this weekend that it would spin off Shearson Lehman. Also, they said, a flurry of arbitrage related sell programs that pounded the general market today accelerated the selloff of American Express, a component of the Dow Industrial Average. American Express fell 3-1/8 to 77-3/8. "It was part programs and part that there was anticipation of an announcement of a spinoff or something with Shearson this weekend, and that announcement never happened," one trader said. In the last few minutes of trading on Friday, another trader said, the stock jumped to close up 3-3/8, largely on anticipation that the company would make a weekend announcement.