Seven American prisoners of war were discovered alive in a town north of Baghdad yesterday. The Marines said they were led to the POWs by Iraqi soldiers who had been abandoned by their own officers. It appears the POWs were not mistreated. Meanwhile, two members of Médecins Sans Frontières have returned to Baghdad after being arrested and held for eight days in an Iraqi prison. They were accused of being spies. They were not physically mistreated, but they say they did hear other prisoners being beaten.