The agency has been trying to conduct the test, which would be the first of its kind in two years, since the middle of last week, but has already put it off three times due to bad weather at launch sites.

"The missile defense test planned for (Sunday) evening has been postponed due to a malfunction of test range safety equipment at Kwajalein Atoll," said Rick Lehner of the Missile Defense Agency.

"Contingent on acceptable weather and repair of the safety equipment, the test could take place Monday evening."

Lehner said a radio transmitter used to send signals to missiles in flight was not working.

"I want to emphasize, it's not a part of the missile defense system, just part of the range infrastructure," he said.

The plan is for an interceptor missile to be fired from Kwajalein Atoll in the Marshall Islands into the path of a target missile launched from Kodiak Island, Alaska.

The test could result in an intercept, but the Missile Defense Agency says the aim is to gather data in preparation for a fully-fledged intercept attempt next March or April.

In earlier tests, target missiles have been successfully intercepted in five out of eight attempts.

But since the last test in December 2002, flight tests have been delayed or cancelled six times, adding to questions about the viability of the system.

Despite the lack of recent flight tests, President George W. Bush is expected to declare the system operational by the end of this year.

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