The announcement is the first time Bush has defined what the first stage would be and committed to when it would be in place.
Pentagon officials stressed that the system's capabilities would be very limited at first, aimed largely at knocking down North Korean missiles. Many more years of development and testing would be necessary, they said, to provide the country with a comprehensive anti-missile shield. Critics, meanwhile, say moving ahead is premature.
Bush's initiative significantly expands previous plans, which called only for a testing site at Fort Greely, Alaska, by the time of the next presidential election.
Essentially, Bush has decided to turn the test facility into an actual missile defense site and also equip Vandenberg Air Force Base in California with some interceptors to shoot down enemy warheads on long-range rockets. The Pentagon will also step up efforts to deploy ship-based and land-based interceptors to defend against shorter-range missiles.
Defense officials said the administration would seek an extra $1.5 billion over the next two years, on top of $16 billion previously projected for this and other missile-defense projects.
Boeing has a $6.4 billion, five-year contract to manage the system's development with companies such as Raytheon, TRW, Orbital Sciences and Lockheed Martin.
Defense Secretary Donald Rumsfeld described the first stage as "better than nothing," saying it's important because "you have to put something in place and get knowledge about it and experience with it."
White House officials said the announcement was made now because the fiscal 2004 budget is being prepared for submission to Congress early next year. Despite some recent setbacks in missile-defense development and testing, Pentagon officials expressed confidence in their ability to build a workable, if limited, anti-missile shield.
Bush and senior aides have warned repeatedly about growing missile threats from North Korea and Iran. Recent reports of a North Korean effort to develop nuclear weapons have added to tensions, but White House officials said Bush's decision was not linked to the latest North Korean developments.
Critics slammed the move as premature and likely to waste billions of dollars on inadequate technology. Sen. Carl Levin, D-Mich., outgoing chairman of the Armed Services Committee, said it "violates common sense by determining to deploy systems before they have been tested and shown to work."
Lisbeth Grunland, a physicist with the Union of Concerned Scientists, said: "They're in the middle of research and development and still lack many of the elements needed for the system. The danger also is that they're not going to do the other things they should be doing to deal with emerging threats, like negotiate with North Korea and get a handle on the spread of fissile material."
In a test last week, the proposed interceptor failed to separate from its booster shortly after launch from an island in the central Pacific.
Lt. Gen. Ronald Kadish, head of the Pentagon's Missile Defense Agency, cited four previous successful attempts and a total record of five hits in eight attempts since testing began in 1999. He said the tests, along with others involving shorter range interceptors, have demonstrated the feasibility of using a missile to hit a missile, a concept known as "hit to kill."
"When you look across the board, we have made, I think, significant progress in our overall hit-to-kill technology," Kadish said. "And that's why we have gained the confidence that we could take this next, modest step."
The plan calls for putting six land-based interceptors at Fort Greely and four at Vandenberg in 2004. Ten more would be added at Fort Greely in 2005. The interceptors would be giant booster rockets designed to soar into space and release "kill vehicles" programmed to home in on long-range enemy warheads and obliterate them by the sheer force of collision.
In addition, up to 20 smaller interceptors would be placed on three Navy ships for use against short- and medium-range missiles.
To detect and track enemy missiles, the Pentagon is building a high-resolution X-band radar that will be placed at sea and a new system of space satellites known as SBIRS-High. The plan also envisions employing as many as 15 Navy ships equipped with Aegis defense systems and SPY-1 radars.
The administration has requested use of early warning radars in Britain and Greenland that would be upgraded with advanced tracking capabilities. These radars, slated to be incorporated into the missile-defense system in 2005, would be especially critical for monitoring missiles launched from the Middle East, officials said.
Bush took office intent on pursuing a workable anti-missile system, something that has eluded U.S. presidents for several decades. He launched the Pentagon on a broad program of experimentation to devise systems for combating enemy missiles in all phases of flight, from shortly after launch to the final seconds before impact.
With the demise of the 1972 Anti-Ballistic Missile Treaty last summer, military planners have been free to explore previously prohibited types of interceptors and radars. But in recent months, Rumsfeld and Kadish have moved to focus the program on the most promising missile defense elements, a move urged last summer by a Defense Science Board panel of senior advisers.
Plans to experiment with a space-based laser have been canceled. A proposed airplane-mounted laser also is experiencing delays. And the timeline for fielding some kind of weapon for intercepting long-range missiles shortly after launch in their "boost phase" has shifted beyond 2008.