Mayor Greg Nickels of the US city of Seattle and King County Executive Ron Sims faced some tough hypothetical decisions after the mock explosion of a radioactive "dirty bomb" in a car in an industrial lot.

　　As events unfolded on Monday in the first day of a five-day national bioterrorism exercise for hundreds of emergency workers in the United States, officials were faced with such questions as whether to declare a state of emergency and how to determine the range of the radioactive plume and alert those who could be affected.

　　The drill, combining the Seattle disaster with a mock bioterror attack in Chicago, is aimed at testing the readiness of local, state and federal authorities. It is the nation's first large-scale counterterrorism exercise since the attacks of September 11, 2001.

　　The idea, Nickels said, is for regional and national agencies to see where strengths and weaknesses lie.

　　"When a disaster occurs, people do not call the White House," Nickels said. "They call 911." That is the emergency telephone number known to all Americans.

　　The mayor said he spoke twice on Monday with Homeland Security Secretary Tom Ridge, and once with Health and Human Services Secretary Tommy Thompson.

　　Once all the data are analyzed the Seattle leaders say they'll determine what they learned.

　　The exercises, which are being headed by the Homeland Security Department, will cost an estimated US million and involve more than 8,500 people from 100 federal, state and local agencies, the American Red Cross and the Canadian government.

　　The drill was being run by about 80 federal workers from a hotel ballroom in Washington. Computers projected maps of Seattle and Chicago onto large screens.

　　Over the next few days, a number of "patients" are to show up at hospitals in the Chicago area, suffering from flu-like symptoms. In the script, a terroristsgroupsreleases a deadly plague in aerosol form.

　　About 200 firefighters and 60 police officers participated. Ten police and 20 fire personnel, among the first on scene, had to be decontaminated for imaginary exposure to radioactivity.