Air Force Lieutenant General Henry Obering, director of the Missile Defense Agency, said the program to field a system capable of intercepting long-range ballistic missiles was going through "a period of disappointment."

"The hard things with missile defense we are accomplishing. The easy things is what we are having trouble with," he told reporters.

The interceptor missile has now failed to launch in two successive tests because of what officials described as relatively minor glitches.

Obering said that in the latest test on February 14 the interceptor missile shut down when a support arm in the silo failed to move out of the way prior to launch.

Three arms are positioned around the interceptor missile in the silo, and just before launch they are lifted out of the way like a drawbridge, he said.

"In the case of the last flight test in February one of those arms did not completely clear, and therefore the signal was sent to the fire control system to stop the launch."

A flight test December 15 was aborted when an internal safety device on the interceptor detected an anomaly in electronic message traffice between the flight computer and the thrust vector controller, which guides the missile.

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