U.S. OFFICERS SAY TWO-DAY BATTLE KILLS 300 IRAQIS
Gun battles rage for second day between militia force loyal to radical Shiite cleric Moktadr al-Sadr, and US and Iraqi forces in Najaf, raising fears of extended battle that could undermine Iraq's new interim government; incomplete figures are given for US casualties, but commanders say 300 rebels were killed; it is heaviest Iraqi casualty figures in such short period that US has reported since Iraq fell; photos (M)