DIWANIYA, Iraq, March 30 — The first Iraqis walked in off the plains at sunrise, a group of nomads with their camels in tow. Then came a young farmer, bearing a white flag. "I have come to get water," said the man, Khalid Juwad, staring into the rifles of several young marines. "I am willing to cooperate." And so the Americans lowered their guns, and Mr. Juwad walked across the front lines, becoming one of the first Iraqis to meet American soldiers here in something other than combat. With so much of the American effort spent racing across empty deserts,...