Los Angeles ? An interceptor missile destroyed a mock warhead Friday over the Pacific Ocean in a key test of the nation’s missile defense system, U.S. military officials said.

It was the most realistic test of the systems that would be used against an attack, said Missile Defense Agency spokesman Rick Lehner.

The 54-foot interceptor shot out of an underground silo at Vandenberg Air Force Base on the central California coast at 10:39 a.m., 17 minutes after the mock warhead was launched from Kodiak Island, Alaska, Lehner said.

The interceptor carried a refrigerator-sized “kill vehicle” that locked on to the approaching mock enemy missile and flew into the 4-foot-long warhead at 18,000 mph.

Lehner said both disintegrated more than 100 miles above the Earth and a few hundred miles west of Vandenberg. The interceptor’s flight lasted 13 minutes.

The $85 million test was designed to see whether the “kill vehicle” could get close to the warhead to test the tracking and sensor systems that would be used in an actual missile attack.

“It gave us a good chance to measure overall system performance. It was the most operationally realistic test we’ve had,” Lehner said.

The interceptor was launched by remote control from a command center in Colorado. The test also was the first use of an early warning radar at Beale Air Force Base, Calif., to provide the data required to put the interceptor on a proper path toward its target.

More than $100 billion has been spent on America’s missile-defense system since 1983 and it has been the subject of criticism by those who call it a costly boondoggle. There also have been allegations that early tests were rigged or their success exaggerated.

The Pentagon says the technology used in those tests is not part of the current research program.