WASHINGTON — Top Pentagon officials have grown increasingly confident in the nation's missile defense system at a time when North Korea is threatening to conduct a long-range launch, leading to speculation of a possible showdown in the exosphere.
Though military officials said a clash between missiles of opposing nations was unlikely, preparations for possible action are at the most advanced stage yet. That is in part because of fears that a North Korean test as early as this weekend could involve a missile directed toward Hawaii.
The communist regime launched seven ballistic missiles Saturday into waters separating the Korean peninsula and Japan. The South Korean government said the missiles flew about 250 miles.
North Korea also launched four short-range missiles on Thursday, although there have been fewer signs in recent days of pre-launch activities pointing to a missile capable of intercontinental reach.
Citing a potential threat to Hawaii, the U.S. last month deployed a gigantic sea-based radar system that officials say can guide underground interceptor missiles in Alaska and California toward long-range missiles in flight. The military also has intermediate-range land-based missiles, as well as specially equipped ships from which interceptors could be launched.
Last month, the vice chairman of the Joint Chiefs of Staff, Marine Gen. James Cartwright, said he was "90%-plus" confident in the ability of the U.S. missile defense system. And Defense Secretary Robert M. Gates said there was a "high probability" the system would work if used.
In 2006, the Pentagon had played down expectations that it might use its missile defense system to try to cut short a North Korean launch that ended up failing on its own. Much of the increased confidence this time around is due to recent advances in radar, along with a record of successful tests and an increased number of interceptor missiles.
Henry A. "Trey" Obering III, a retired Air Force lieutenant general who stepped down from the Missile Defense Agency late last year, said the radar system sent to Hawaii had significantly expanded U.S. defensive capabilities.
The system is known as sea-based X-band radar, a reference to the electromagnetic frequency at which it operates. The higher frequency provides more detailed resolution than other radar and enables interceptor missiles to distinguish between lethal weapons and decoys or other debris.
Developed at a cost of about $900 million, the system looks like a giant white ball mounted atop a modified oil-drilling platform that can be moved around. The X-band system is based in Alaska and has made previous trips to Hawaii.
In 2006, the radar could be used to track incoming missiles but not to intercept them. But in tests late last year, the Missile Defense Agency used the X-band for the first time to guide the interceptors to their targets. The successful tests and use of X-band radar have proved the ability of the system, Obering said.
"That is a tremendous demonstration of capability that adds to the level of confidence," he said.
Three months ago, Gates tamped down speculation that the U.S. would try to interrupt what North Korea said was a satellite launch but what many U.S. experts considered a long-range missile test. Then, in June, he expressed optimism about missile defense capabilities.
Since the "Star Wars" plans of the Reagan administration, U.S. officials have spent more than $100 billion on missile defense weaponry and electronics. The Pentagon now maintains about two dozen interceptors in silos at Ft. Greely, Alaska, and at Vandenberg Air Force Base in California that are more advanced than earlier versions.
"One of the key lessons we learned from every war game we ran was that the more interceptors you have, the better off you are," Obering said.
Still, many experts and critics of the missile defense system think the confidence is misplaced. "It is completely unwarranted, and it is a wild speculation based on assumptions that are almost certainly untrue," said Theodore Postol, an MIT professor who has studied the system.
Despite Pentagon claims of technological advances, for example, Postol argued that the U.S. interceptors would have a difficult time telling a missile warhead from "countermeasures" -- decoys or other debris meant to fool the interceptors.
Critics also consider the North Korean threat overstated, especially given the long-standing inaccuracy of Pyongyang's missiles and the fact that they are not equipped during test launches with any kind of warhead, nuclear or nonnuclear.
"Why would you want to shoot at it? It is not armed with a nuclear weapon, and it is going to land in the ocean," Postol said. "What we are talking about is shooting at a missile that is not a threat with a missile that can't intercept it."
But backers of the system believe hitting North Korea's test missiles, even if there is no security threat, would prevent Pyongyang from acquiring crucial knowledge from a test.
"If you shoot it down, they are not going to know where their technology is and they aren't going to be able to increase their capability," said Riki Ellison, chairman of the Missile Defense Advocacy Alliance.
Using the interceptors against a real North Korean missile would quiet many critics if it worked but expand the challenges facing the system if it failed.
"This would be a really realistic test," Ellison said.