HONOLULU - A drill planned to demonstrate the US Navy's ability to knock down two incoming missiles at once from the same ship failed off Hawaii's coast on Thursday, the US Missile Defense Agency said.

This photo provided by the Department of Defense shows a Standard Missile-3 interceptor being launched from the guided missile cruiser USS Lake Erie in the Pacific Ocean off Hawaii March 8, 2006. [AP]

A computer configuration problem aboard the USS Lake Erie grounded one interceptor missile, and officials halted the second during the test of the sea-based US missile defense system.

It was the second failure in nine tests of the system by the agency and the US Navy, said Missile Defense Agency spokesman Chris Taylor.

The US Pacific Fleet has been gradually installing missile surveillance and tracking technology on many of its destroyers and cruisers amid concerns about North Korea's long-range missile program.

In Thursday's drill, a dummy enemy ballistic missile was launched from the Pacific Missile Range Facility on Kauai, simulating a missile attack on US territory, and a shorter-range missile was fired from a Navy aircraft and aimed at the anti-missile ship, the Lake Erie, the agency said.

Both target missiles dropped harmlessly into the ocean.

Missile defense officials say the US missile defense system already being installed on ships is still viable, and they are planning a repeat of the dual-launch test, probably sometime next year.

Riki Ellison, president of the Missile Defense Advocacy Alliance, based in Alexandria, Va., said, "Though this event is discouraging, the testing enables our defenses to be more efficient and more effective."