The Dow Jones industrial average ended down less than 2 points, after dropping nearly 30 points earlier in the day. Volume was heavy with more than 400 million shares traded. At 3 p.m. on Wall Street, the Dow Jones industrial average was off 15.90 at 5,570.16, above its worst levels of the day. Volume was heavy at the New York Stock Exchange, with 438.16 million shares traded, up from Thursday's pace. The NYSE composite index was down 0.53 at 342.87, the Standard & Poor's 500 composite was down 0.49 at 640.30, the American Stock Exchange's market value index was up 0.74 at 562.52, and the Nasdaq composite was up 7.07 at 1,098.14. The 30- year benchmark Treasury bond was extending its losses, down 5/8 point and yielding 6.74 percent.