The Environmental Protection Agency urged school officials Thursday to test all school buidings for radon, saying preliminary tests from 16 states show many schools have unhealthy levels of the cancer-causing gas. EPA Administrator William Reilly said although the test results were only preliminary, the levels found were high enough to warrant nationwide testing of school buildings. "It is important that school administrators nationwide understand both the seriousness of the risk and the relative simplicity of testing and fixing the problem," said Reilly.