WASHINGTON - The Pentagon set a July 7 target date for a $100 million test of an anti-missile shield, while leaving open the possibility that Defense Secretary William Cohen could recommend proceeding with deployment of the controversial system by 2005 even if the July test is a failure.
''The July test will be our most demanding trial to date,'' Cohen said in a written announcement of the twice-delayed test. This will be the first flight test to incorporate a communications link from ground radars to the missile interceptor in flight, providing last-minute guidance on where to find the target in space.''
Jacques Gansler, the Pentagon's technology chief, acknowledged Tuesday that the Pentagon's scientists and engineers are pushing the envelope of technological know-how in trying to shoot down long-range ballistic missiles in space - a goal the United States has pursued, off and on, for more than two decades.
''It's clearly a high-risk overall program,'' Gansler said, referring to the possibility of setbacks. ''And it's not a high probability of being able to precisely get everything to work on this flight'' in July.
The Pentagon has said it wanted to score two missile intercepts before continuing toward deployment. It managed one intercept last October, but the most recent test, in January, missed its target.
Asked whether a failure in July would preclude Cohen recommending to President Clinton that he keep to the schedule for deploying a limited missile defense by 2005, Gansler said, ''It depends what type of failure it was.'' At any rate, he added, it will be a decision for Clinton based on factors beyond the technical aspects.
Clinton, who is scheduled to decide this fall whether to give the go-ahead for starting construction on a high-powered missile defense radar on the Alaskan island of Shemya, has said he also will consider such factors as cost, the global threat of missile attacks on U.S. soil and the impact on arms control.
If the July test goes as planned, a modified Minuteman II missile will launch from Vandenberg Air Force Base, Calif., on July 7 and head west. Cued by high-speed computers at Colorado Springs, Colo., a single interceptor rocket will be fired from Meck Island in the Pacific in pursuit of the target. A 130-pound ''kill vehicle'' will release from atop the interceptor rocket and maneuver into the path of the target 144 miles above Earth, colliding with the mock warhead at a speed of 12,000 miles an hour and destroying it.
The last such intercept attempt failed in January because the mechanical ''eyes'' aboard the ''kill vehicle'' did not work right. Because of the work needed to fix that problem, the following test was delayed from April to July.
Critics say the concept of intercepting long-range missiles outside the Earth's atmosphere is flawed because decoy launches could fool the U.S. interceptor. The Pentagon acknowledged decoys present a long-term challenge, but said the system can overcome the crude decoys likely to be encountered in the short run.
Asked to respond to such critics, Gansler said, ''They're wrong.'' He noted that a panel of independent experts recently concluded in a classified report to Cohen that the program is on track to achieving its goal, although it may take longer than planned.
Tuesday, the Pentagon released an unclassified summary of that report, dated June 13. It said technology ''is available'' to field a limited system of missile defenses. It cautioned, however, that the Pentagon must prepare for the more sophisticated decoys likely to emerge in the future.
While there is a ''high risk'' that the system may not be ready for use by 2005, there is ''no technical reason to change the schedule at present,'' the summary said.
That is a key point, because the schedule is at the heart of much of the debate over the missile defense project.
The idea is to use a combination of powerful radars, ground-launched missile interceptors based in Alaska, and high-speed computers to protect all 50 states against an attack by 30 or fewer long-range missiles. The Pentagon estimates this will cost $36 billion, including the cost of operating it for 20 years.
To have the system ready for use by 2005, Clinton needs to give the go-ahead this fall to award contracts for starting construction of the high-powered radar on Shemya Island next summer. The Pentagon has set other key milestones, including a decision in the summer of 2003 on whether to go ahead with building the actual missile interceptors that would be based in underground silos near Fairbanks, Alaska.
That 2003 decision, Gansler said, ''is the real decision in terms of commitment to building weapons.''
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