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 about missile defense we are accomplishing. The easy things is what we are having trouble with, like arms moving out of the way," 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. 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," he said.

Experts still do not know why the arm failed to retract, or what the implications are for the eight interceptor missiles already installed in silos in Alaska and California.

"I'm very, very disappointed in this last test because of the simplicity of the failure, and the fact that it was a glitch that really got in out way," the general said said.

A flight test on December 15 was aborted because of a software glitch.

The interceptor missile shut down in that test when an internal safety device on the interceptor detected an anomaly in electronic message traffic between the flight computer and the thrust vector controller, which guides the missile.

Obering said he has chartered an independent review of the testing program to try to determine why the failures weren't caught in time, and how they can be prevented in the future.

He also appointed Rear Admiral Kathleen Paige, who heads a separate program to develop a sea-based missile defense system, as director of mission readiness to get the testing program for the ground-based system back on track.

The next flight test could be held as early as the end of April if the underlying cause is identified quickly, he said.

The Pentagon had expected to put the ground-based missile defense system into operation by the end of last year, but that has been delayed indefinitely.

Obering, however, said missile defense crews in Alaska and California can now shift the ground-based system from a test mode to an operational posture in a matter of minutes as a result of "shakedown" exercises.

"When we started the process back in October it was taking us hours to be able to make that transition. We've worked that down to minutes, and we continue to refine the procedures for that," he said.

The February 14 flight test was not a complete loss, according to Obering.

Radar and other sensors tracked a target missile that was fired from Kodiak Island, Alaska. Fire control computers generated a "weapons task plan" that was relayed and accepted by the interceptor missile before it shut down.

Obering also highlighted the successful intercept on February 24 of a short range missile by a Standard Missile-3 interceptor fired by Aegis destroyer in the Pacific.

It was the fifth successful test of the sea-based system. But it marked the first use in a test of operational versions of the SM-3 missile and the Aegis missile defense system.

Paige said the Aegis destroyer received no warning of the missile shot, which was fired from just over 100 miles away.

"We hit the warhead of the threat missile right where we needed to, right where we expected to," she said.

The test was the centerpiece of a three week naval exercise called Stellar Dragon which involved a mock war a sea with two Aegis warships, submarines and gunboats.

It has come amid tensions with North Korea, which said this week that it was no longer bound by a moratorium on missile tests that it has observed since September 1999.

Paige said the navy has four operational SM-3 missiles available in case of a crisis.

"If called upon in an emergency, that system can deploy and defend against short, medium range ballistic missiles," Paige said.

"The hammer isn't cocked but if you cock it, they will be loaded," she said.

Seven Aegis warships have been modified for missile defense missions, several of which are stationed in the western Pacific. Obering said they are equipped to track missiles with their Spy-1 radars but not to engage them.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.

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