Lt. Col. Jay Smith, chief of staff for the U.S. Army's site activation command, confirmed Monday that the booster was flown into Eielson Air Force Base and trucked down the Richardson Highway to Greely.

The three-stage booster will now be outfitted with a "kill vehicle"--a small, super-fast rocket designed to smash any warhead launched by an enemy missile.

The Bush administration plans to have at least six such interceptors in working order at Fort Greely by the end of the year, with plans for 20 more over the next few years.

Rick Lehner, spokesman for the Missile Defense Agency in Washington, said the first six interceptors should arrive once every few weeks over the course of the summer.

Maj. Eric Maxon, spokesman for the site activation command, said the military will not provide advance notice of booster arrivals for security reasons.

The military flew the first booster to Eielson because Fort Greely's airfield cannot support heavy planes.

According to last year's environmental impact statement on the missile defense system, the interceptors are about 54 feet long and 4 feet in diameter, and weigh up to 25 tons. They hold about 45,000 pounds of solid propellant.

Lehner said they are not large enough to create a traffic problem during transportation.

The booster will be placed in an underground silo but that won't happen immediately, Maxon said.

"It still has to go through all the procedures to get it ready for emplacement," he said.

The booster was built by Orbital Sciences Corp., said Barry Beneski, company spokesman in northern Virginia. Orbital and Lockheed Martin are building booster rockets for Boeing, the military's main contractor on the missile defense system.

The kill vehicle, which rides the booster into outer space before separating, is built by Raytheon.

A ceremony to mark the end of construction on the initial six silos will be held Saturday, Maxon said.

At Fort Greely, the military is preparing two pads with a capacity of 20 interceptors each, Maxon said. The hardware for the first pad, with the six silos, is complete. The next 10 interceptors, for which Congress has already provided money, will go in the second pad.

Although the military conducts regular interceptor tests around the Pacific Ocean, it has no plans to launch any from Fort Greely except in a real attack.

Lehner said Monday that may change in the future if designers decide test launches from Fort Greely are necessary. If so, any proposal would have to undergo a variety of studies. The military does plan to launch test targets, including one later this summer, from the state-owned launch facility on Kodiak Island.

A spending bill passed by the U.S. Senate last week would give about $10.2 billion to missile defense programs during the 2005 fiscal year. About half of that would go toward developing the ground-based, midcourse system, whose interceptors are based at Fort Greely.

Using that system, the military plans to shoot down any intercontinental ballistic missiles headed toward the United States. The interceptors rising from Fort Greely and other sites would attempt to strike any enemy warheads as they travel through their "midcourse"--gravity-free outer space.

Critics say the concept has fatal strategic and conceptual flaws and is far too expensive. Supporters say missile defense is essential for the country's security and Missile Defense Agency officials say they are confident that technical challenges can be overcome.

Last week, the Senate proposed to add about $163.5 million to the amount the Bush administration had requested for the midcourse segment. The money includes $22 million to continue upgrading Fort Greely's Allen Army Airfield as well as another $100 million for "GMD enhancements."

Lehner said enhancements could include "anything from software upgrades to hardware modifications." Because there is no final design for the system, "that's going to be a continuing process."

Lehner said most of the $100 million would probably be spent outside Alaska on improving the interceptor design and communications systems, although some could be spent at Fort Greely and Eareckson Air Station on Shemya Island in the Aleutians, where the military is upgrading a radar so it can better detect incoming missiles.

The House of Representatives and Senate spending bills must be rewritten into a final version for the president to sign. Sen. Ted Stevens, R-Alaska and chairman of the Senate Appropriations Committee, will sit on the conference committee that writes the final bill.

Washington, D.C., reporter Sam Bishop can be reached at sbishop@newsminer.com or (202) 662-8721.