The teeming Swift & Co. slaughterhouse on the edge of town has the feel of a military base lately. Security cars cruise the fenced compound, and periodic drills are run to prepare for any attack. At the Wayne Farms poultry plant in Decatur, Ala., armed guards patrol the grounds, searching for any threat to the tens of thousands of chickens. In Porterville, Calif., dairy farmer Tom Barcellos recently installed video cameras in his milking barns to keep watch over his 1,200 cows. Nothing seems farther from the front lines of terrorism than the vast American hinterlands, yet since the Sept. 11attacks, they have been drawn into the amorphous battle. The threat is agroterrorism — the use of microbes and poisons to shake confidence in the U.S. food supply and devastate the $201-billion farm economy. Diseases such as swine fever or citrus greening can spread across the land silently. A single outbreak of foot-and-mouth disease could require the destruction of millions of cows and result in a worldwide ban of U.S. cattle exports for years. “The animal becomes a weapon,” said Peter Chalk, an agroterrorism expert at Rand Corp., the Santa Monica-based think tank. About OODA Analyst