The medical detectives at the Atlanta-based Centers for Disease Control have a well-earned reputation for relentlessly tracking down the causes of such mysterious ailments as Legionnaires' disease. But the agency's record is in danger of being blemished by a bitter controversy over Agent Orange, a defoliant containing dioxin, a suspected carcinogen.

Critics charge that the agency and one of its senior officials, Dr. Vernon Houk, helped scuttle a $63 million study that might have determined once and for all whether U.S. troops exposed to Agent Orange suffered serious damage to their health. Houk maintains he recommended that the study be canceled...