Demonstrating the capabilities of the ground-based system the United States wants to deploy to Poland and the Czech Republic, the Pentagon said its forces successfully conducted a ballistic missile defense test over the Pacific on Friday.

According to senior defense officials, the test demonstrated the ability of four separate radar systems to work together and direct a kill vehicle into the path of an incoming missile 1,300 kilometers away, and 200 kilometers high, traveling at 10 kilometers per second.

However, a key part of the test did not go as planned - officials say a missile launched from California hit a target that had been launched from Alaska 29 minutes earlier.

The target missile, a 40-year-old Cold War relic, failed to deploy the decoys that were designed to stress the intercept system, and determine whether it can differentiate between the real warhead and the decoy.

Yesterday's test was the 13th of its kind by a ground-based interceptor since 1999. According to Pentagon spokesman Bryan Whitman, eight such tests, including the one yesterday, have succeeded in destroying the target missiles; the last one was in September 2007.

The Missile Defense Agency said the test - which cost about $120 million - was aimed at "the type of long-range ballistic missile that could be used to attack the nation with a weapon of mass destruction." At a Pentagon news conference, Lt. Gen. Patrick O'Reilly, chief of the agency, said: "It was the largest, most complex test we have ever done."

Nonetheless, the missile defense program has come under criticism for two main reasons - its expense and the questions about its ability to discern decoys.