(AP)U.S. Army ground forces attacked Republican Guard units Tuesday near Karbala, scarcely 50 miles from Baghdad, part of around-the-clock combat pointing toward an assault on the capital. An American POW was rescued in Iraq. Defense officials said Army units attacked elements of the Medina Division of the Republican Guard in the clash near Karbala, hitting an elite Iraqi force weakened by heavy air bombardment over several days. Pfc. Jessica Lynch, a 19-year-old supply clerk from Palestine, W. Va., was the POW freed after nine days in Iraqi hands. Neither her condition nor the details of her rescue were immediately available.