The tests were to have been held this winter and spring.
Air Force Lt. Col. Rick Lehner, spokesman for the Missile Defense Agency, said there will not be another intercept test until Boeing Co., the lead contractor, has a newly designed rocket booster ready for use this autumn.
"The feeling is that we need to concentrate on the booster this year because it is behind" schedule, Lehner said.
The MDA blamed the failure of a test last December on a substitute booster rocket that has been used in tests to date. It was the second failure pinned on the booster rocket.
Pentagon officials have said they are confident that their basic approach to intercepting enemy warheads during their flight through space — known as "hit to kill" technology — has been proven to work in previous tests. What has been lacking is the new booster that launches the "hit to kill" technology into space.
Boeing originally was to begin flight tests of a new booster — used to carry a missile-intercept device known as a "kill vehicle" into space to destroy an enemy warhead by colliding with it — in 2000, but it encountered technical problems. After a booster launch failure in December 2001, Boeing decided to contract with Lockheed Martin, and later Orbital Sciences, to come up with new designs for an intercept booster.
The goal all along has been to develop a new-generation booster designed specifically for missile defense.
In announcing last month how his agency intends to meet President Bush's goal of having an initial missile defense system ready to field by the end of 2004, Air Force Lt. Gen. Ronald Kadish told reporters he was concerned about the booster problem.
"I don't like where we are in terms of being developed with the boosters," Kadish said. If Boeing fails to come up with a useable booster by next autumn, the overall missile defense program will suffer, he said.
"We can't use an interceptor that doesn't fly right," he said.
Lehner, spokesman for Kadish's agency, said that forgoing the intercept tests that had been scheduled for this winter and spring will save not only the $200 million it costs to conduct the tests but also the "kill vehicles" that are used, and thus destroyed, in the tests.
The Pentagon has been successful in four of its last five missile intercept tests and five of its last eight.
But the success of one of those tests is another sticky issue for the missile defense program: A professor at the Massachusetts Institute of Technology has alleged that a laboratory at MIT improperly certified that a 1997 test declared successful had actually failed.
Last month, the Boston Globe reported that an MIT review has called for an outside investigation. The professor involved, Theodore Postol, is requesting a congressional probe.