The successful exercise was a big deal for the Missile Defense Agency, in part because two recent back-to-back tests of a land-based interceptor failed. The last, on Feb. 14, saw a target missile launched from Kodiak Island, Alaska, but the interceptor failed to launch, just as it had in December.

The controversial U.S. missile defense program is opposed by many countries that fear it could trigger a new arms race. There also are questions about whether it's necessary in a post-Cold War climate.

Just yesterday, Canadian Prime Minister Paul Martin announced that his country will not sign on to the U.S. missile defense program.

During yesterday's test, the target rocket was fired from the sand dunes of Kaua'i's Pacific Missile Range Facility at 11:03 a.m. The Lake Erie, equipped with the Aegis radar system, tracked the launch and received information on the rocket's trajectory via satellite from the distant Aegis destroyer USS Russell.

Air Force Lt. Gen. Henry "Trey" Obering, director of the Missile Defense Agency, said the cruiser launched its interceptor about a minute after the target launch. The Standard Missile-3 interceptor collided with the target about two minutes later as it was descending just outside the Earth's atmosphere.

The test was impressive enough to move the Navy to start installing the system on ships, even though it is still being tested, said John Young, assistant secretary of the Navy for research, development and acquisition.

"It's an interim capability and it's available," said Young, who compared the intercept hitting a basketball traveling at 3,600 mph with another basketball.

Sixty-eight U.S. Navy cruisers and destroyers have Aegis Weapon System capabilities, and plans are under way to install the system on 18 more destroyers.

The SM-3 would protect allies or U.S. forces from short-range ballistic missiles launched over a body of water. Potential scenarios include missiles fired by North Korea at Japan, or by China at Taiwan.

Young said the Navy made its test as realistic as possible. The USS Lake Erie crew was watching for missile launches without much support from contractors and Naval weapons experts.

"It was a tactically realistic scenario. The crew was in a search mode and was not aware of the actual launch time," he said.

The Missile Defense Agency and the Navy cooperatively manage the Aegis Ballistic Missile Defense Program. The sea-based system is part of a larger national missile defense system that includes land-based, aircraft-launched and mobile interceptors.

Lockheed Martin Maritime Systems and Sensors of Moorestown, N.J., is the system's prime contractor. Raytheon Missile Systems of Tucson, Ariz., is the prime contractor for the SM-3.