WASHINGTON — The U.S. Missile Defense Agency (MDA) is insisting that the failed test Dec. 15 of the interceptor for the fledgling national missile shield will not affect the timetable for putting the system on alert.

Longtime critics of the U.S. government’s stated plan to put the system on alert before the end of the year pounced on the failure as evidence that the schedule was technically unjustified. Even some missile defense advocates said the Defense Department should at least figure out what went wrong before declaring that the United States has a limited capability to defend itself against missile attacks.

But Rick Lehner, a spokesman for the MDA, on Dec. 17 reiterated the agency’s position that no single flight test would determine whether the Ground-based Midcourse Defense system is ready. That decision, he said, would be made not by the MDA but by the president or secretary of defense based on recommendations from the leadership of the Pentagon’s Northern, Pacific and Strategic commands.

The Ground-based Midcourse Defense system, which today consists of six interceptors at Fort Greely, Alaska, and one at Vandenberg Air Force Base, Calif., is undergoing what the MDA refers to as shakedown testing to determine its readiness for action. Even before the test failure, the MDA said it would not necessarily meet its stated goal of declaring the system operational before the end of the year.

The officials evaluating the system’s readiness will not necessarily wait for the results of the investigation into what went wrong on Integrated Flight Test 13C before making their recommendation , Lehner said. That investigation has begun and likely will take weeks, he said, declining to be more specific.

Integrated Flight Test 13C was to be the first of the specific interceptor configuration now being installed at Fort Greely and Vandenberg. It consists of the Orbital Boost Vehicle built by Orbital Sciences Corp. of Dulles, Va., and the Exoatmospheric Kill Vehicle supplied by Raytheon Missile Systems of Tucson, Ariz.

The interceptor was to lift off from the Kwajalein Atoll in the Pacific to engage a target missile launched from Kodiak Island, Alaska. The test called for the kill vehicle to approach, but not necessarily hit, the target.

But while the target vehicle launched without a hitch, the interceptor never took off due to an as yet unknown problem. MDA and its contractors are reviewing the pre-launch data in an effort to establish a timeline of events that might point to the cause of the failure, Lehner said.

The test has not been rescheduled, Lehner said.

Klaus Heiss, co-founder of High Frontier, a missile defense advocacy group based in Arlington, Va., characterized the test failure as trivial, but said the MDA nonetheless needs to iron out the issue and repeat the test before declaring the system operational.

George Landrith, president of Frontiers of Freedom, a political advocacy group based in Oakton, Va., agreed that the Pentagon’s first order of business is to demonstrate that it has fixed the problem that prevented the interceptor from taking off. He said he expects the Ground-based Midcourse Defense system to be ready to go on alert shortly thereafter .

The threat posed by ICBMs justifies putting the system on alert even before it has been fully tested, Landrith said. “It won’t do to sit on our hands,” he said.

Baker Spring, a senior analyst with the Heritage Foundation in Washington, said if the problem that marred the test turns out to be minor, it may not be necessary to successfully carry out Integrated Flight Test 13C before putting the missile shield on alert, especially if the ongoing shakedown tests do not turn up any major command and control issues. He said that in an actual attack, a minor problem that prevents an interceptor from launching likely could be overridden by system operators.

Missile defense critics said the test failure is only the latest piece of evidence that the Ground Based Midcourse Defense system is not ready for prime time. These critics have argued that even a successful Integrated Flight Test 13C would not inspire confidence in the national missile defense shield’s capabilities.

The MDA has yet to conduct intercept tests where the shooters did not have advanced notice of the target’s launch site and trajectory, said Phil Coyle, a former chief weapons tester at the Pentagon. The targets also continue to carry beacons that relay their precise location to the shooters, he said.

The MDA also has yet to test the system night, when the target would be cooler and thus more difficult for infrared sensors to detect, said Coyle, currently a senior advisor to the Center for Defense Information, a think tank here.

Congress has directed the MDA to begin conducting tests under more realistic conditions in 2005, but the agency has yet to set dates for such demonstrations.

Chris Hellman, a military policy analyst at the Center for Arms Control and Non-Proliferation, said the Dec. 15 failure is “just another reason to have no confidence in the system.”

Comments: jsinger@space.com