The United States is conducting what President Bush has described as a preventive war to eliminate Iraq's chemical, biological and nuclear weapons programs. Statements by senior administration officials indicate that the United States may use chemical weapons of its own - so-called "nonlethal" riot control agents - against Iraqi troops if, for example, those troops use Iraqi civilians as human shields. Such actions are unlikely to protect innocent Iraqis from harm. They could also increase the risk to U.S. troops while violating one of the key disarmament agreements that U.S. military action is designed to uphold. In little-noticed testimony Feb. 5, Defense Secretary Donald H. Rumsfeld confirmed before the House Armed Services Committee that the Pentagon has been trying to write rules of engagement that would permit U.S. military forces to use riot control agents (RCAs) in Iraq. Elisa D. Harris is a senior research scholar at the Center for International and Security Studies at the University of Maryland.