Last August, an explosion tore through the Bayer CropScience chemical plant here, killing two employees and raising the fears of residents in what has long been known as Chemical Valley. Now, a federal agency wants to hold a public hearing to lay out its preliminary findings about what caused the accident. But Bayer, citing a terrorism-related federal law, is trying to limit what the agency can disclose. [also refers to Union Carbide (now part of Dow)]