A technical glitch has prompted the Pentagon's missile defense unit to scale back plans for a Friday test of a system designed to shoot down missiles heading for the US mainland. Lt. Gen. Henry A. Obering III, head of the Missile Defense Agency, said Tuesday that there were problems with telemetry cards that record data during tests of the ground-based defense missile system. Chicago-based Boeing Co. is the lead contractor on the project. The problems, which arose from soldering of the cards, means the test will be only a simulation of an interceptor missile striking an incoming missile. The Missile Defense Agency had planned to also use a real interceptor missile to try to shoot it down. Obering said a similar test planned for December is expected to go ahead with a real interceptor.