Immediate plans call for building two $1-billion radar installations and adding 20 rocket interceptors to the 44 already deployed in underground silos at Ft. Greely in Alaska and at Vandenberg Air Force Base in California.

The Pentagon also is taking steps to launch new satellites to help each interceptor's "kill vehicle" find, crash into and destroy incoming ballistic missiles high above the atmosphere.

The expected cost is about $10.2 billion over five years, on top of more than $40 billion already spent for the system. On Thursday, Congress passed a short-term government funding bill that includes $200 million to start preparing construction of additional missile silos in Alaska.

But government reports and interviews with technical experts suggest the planned upgrades, including a redesigned kill vehicle, are unlikely to protect the United States from a limited-scale ballistic missile attack, the system's stated mission.

One concern is the administration's rush to expand the system.