NEW YORK, Sept. 21 (AP) ÛÓThe stock market repeated an old trick today, losing ground in early trading and firming near the close.</br></br>The Dow Jones average of 30 industrials, off over 5 points during the session, ended the day with a .76 loss to close at 939.49.</br></br>This seesaw pattern characterized trading Wednesday and Monday. A slight variation Tuesday saw prices rise during the day only to drop off in late trading.</br></br>Prices dropped for the 14th straight day on the American Stock Exchange, and Over-the-Counter issues also lost ground.</br></br>The Amex price-change index was off .03 to 26.06, its lowest point since Jan. 6. Volume was 2.74 million shares, down from 3.07 million Wednesday.