The test, planned for 0200 GMT Wednesday, comes on the heels of a successful intercept in October that showed that the interceptor's "kill vehicle" was able to seek out and destroy a dummy warhead released by a target missile fired from 4,300 nautical miles (7,900 kilometers) away.

Like the last time, an interceptor missile will be fired from Kwajalein atoll in the Pacific at a Minuteman II missile launched from Vandenburg Air Force Base in California.

Unlike the last time, however, the interceptor missile will be guided into place by battle management computers processing and relaying tracking data from early warning satellites and ground based radars in Hawaii and Kwajalein.

"This is a complex test," said a senior defense official. "There are a lot of elements, a lot of players that have to communicate and coordinate in real time, and ... in less than 30 minutes."

The stakes are also high because President Bill Clinton has said he will decide this summer whether to deploy a national missile defense system to counter what the US military and CIA sees as a growing ballistic missile threat from so-called rogue states.

The military managers of the NMD program have been told they must have two "metal-to-metal" hits and one of them has to be part of an integrated test of the system to pass a defense readiness review in April or May ahead of the president's decision.

Pentagon spokesman Kenneth Bacon was unable to say, however, what technical criteria must ultimately be met for the Pentagon to declare the system ready for deployment.

"There's going to be a lot of room for definition here," he said. "What is clear to me is that this is a very high priority program. We are working very hard in this building to give the president the information he needs, from the technical side, to make a decision sometime this summer."

Besides technical considerations, Clinton will have to weigh the political consequences of ordering the deployment of a national defensive shield capable of intercepting a limited attack by ICBMs with only unsophisticated decoys.

The proposed system has aroused vehement opposition in Russia, which refuses to allow changes to the 1972 Anti Ballistic Missile treaty, and even among some European allies. They argue it will weaken nuclear deterrence and unravel existing arms control regimes.

The technical challenges facing NMD remain daunting, however.

The interceptor missile is fired 20 minutes after the target missile is launched. Two and a half minutes later a "kill vehicle" is released by the interceptor. Closing on the ICBM at a speed of 15,000 miles (24,000 kilometers) per hour, the "kill vehicle" has about six minutes to seek out, identify and destroy the warhead.

"The one thing I would like to impress is this is hard to do," said the senior defense official.

In the last test, the "kill vehicle" failed to calibrate its position by the stars, officials said.

Nevertheless, it was able to maneuver into the path of its target with an onboard inertial navigational system. Using an infrared seeker, it then distinguished between a decoy balloon and the warhead, destroying the warhead.

The test next week will determine whether it can accomplish the same feat using real-time data relayed by a ground-based battle management computer system. Copyright 1999 AFP. All rights reserved. The material on this page is provided by AFP and may not be published, broadcast, rewritten or redistributed.