The Pentagon recently conducted an important test on Friday of the system to defend against long-range ballistic missiles that turned out to be a rated success. The test was conducted to see the effectiveness of the system. An interceptor collided with a mock warhead high over the Pacific.

The target missile was launched from Kodiak Island, Alaska, and tracked by radar at Beale Air Force Base, near Sacramento. The interceptor missile was fired from Vandenberg Air Force Base, north of Santa Barbara, Calif., striking the target warhead about eight minutes later, officials said.

The test was worth $85 million and was replay of one from late May that was not completed because the target rocket fell short of the designated interceptor range in the Pacific. Because the attacking rocket and its mock warhead never reached the area to be defended, the interceptor missile was not launched in that test.

The Bush administration proposes a missile defense system of 40 interceptors at Fort Greely, Alaska, along with 4 at Vandenberg and 10 to be located in Poland. The ground-based interceptors would be guided by a series of radar sites, including one proposed for the Czech Republic.

But efforts to place elements of an American missile defense system at the two Central European sites have angered Russian officials, and the proposed sites face possible budget cuts from skeptical Democrats in Congress.

The administration argues that the system is a limited defense against a small attack from nations like North Korea or Iran and that the small number of interceptors is no threat to the large Russian missile arsenal.