Only a test

A crop duster will spit out a suspicious-looking cloud in rural Oklahoma this spring, but it won't be a terrorist attack; it will be part of the government's attempt to prepare for one.

The Army and the EPA are running the bioterrorism drill, and the crop duster involved will drop harmless powdered clay and grain alcohol. Scientists want to know whether weather radar can detect biological and chemical particles in the air.

So about 600 people near Oklahoma City received letters telling them not to worry if they see a plane releasing a cloud of dust over their heads. Army officials say the materials are all biodegradable and harmless, although the particles resemble those of biological or chemical weapons.

The government originally set the Oklahoma test for last month, but resident complaints delayed the project. Some locals said they would leave town until it was finished.

Crop dusters became a factor in the war on terrorism when intelligence agents discovered that al-Qaeda ringleader Mohammed Atta had tried to buy one. After 9/11, the government grounded crop dusters three times as experts worried that terrorists might try to steal one and use it to spread anthrax or some other deadly agent.

Officials also warn that firefighting planes used by the Forest Service may be tempting to terrorists. Their tanks are about six times larger than that of a typical crop duster.