American forces battled Iraqi defenders in fierce street fighting 50 miles south of Baghdad on Monday, pointing toward a drive on the capital. Army guards shot seven Iraqi women and children to death when their van refused orders to stop at a checkpoint, officials said. U.S. troops and tanks encountered rocket-propelled grenades and small arms fire in a dawn raid against Republican Guard defenders of Hindiyah, a key city astride the Euphrates River. Other units fought to isolate Najaf to the south and prevent attacks on U.S. supply lines.