The Army postponed today its latest attempt to destroy a flying target with an expensive antimissile missile that has never scored a hit.

Today's scheduled trial was put off until Thursday because of a power failure on the base during the night, said spokesman Jim Eckles.

The Theater High-Altitude Area Defense, or THAAD, missile system has cost at least $3.8 billion and critics call it a waste of taxpayers' money. The Defense Department said it needs a new state-of-the-art antimissile missile to protect its troops from missiles that cannot be downed by current weapons.

THAAD's most recent direct-hit attempt, its sixth, failed March 29. Another test was scrubbed May 25 because the target missile malfunctioned.

Secretary of Defense William S. Cohen said he is not discouraged by the problems. "We are, in fact, breaking the barriers of technology every day and we would expect this to go forward, even if we have future failures," Cohen said. "We have to proceed and will ultimately be successful."

Lockheed Martin Missiles & Space was assessed a $15 million penalty for not achieving a hit during the March 29 test. And it must have two successful direct-hit missile tests by June 30 or be penalized an additional $20 million, according to its contract. In all, the company could face up to $75 million in penalties by the end of 1999 if there are more failures.