The Vatican is quietly conducting two sweeping investigations of American nuns, a development that has startled and dismayed nuns who fear they are the targets of a doctrinal inquisition. Sister Sandra M. Schneiders has urged fellow nuns not to participate in the study that is being conducted by the Vatican. Nuns were the often-unsung workers who helped build the Roman Catholic Church in this country, planting schools and hospitals and keeping parishes humming. But for the last three decades, their numbers have been declining – to 60,000 today from 180,000 in 1965. While some nuns say they are grateful that the Vatican is finally paying attention to their dwindling communities, many fear that the real motivation is to reel in American nuns who have reinterpreted their calling for the modern world.