In an Eye on America investigation, CBS News National Security Correspondent David Martin reports data from tests of the system show a possible Achilles' heel: an inability to distinguish between missiles and decoy balloons that enemy missiles could dispense to confuse the missile defense system.
The National Missile Defense (NMD) is designed to foil limited missile attacks from rogue nations. Russia and some U.S. allies say it violates the 1972 Anti-Ballistic Missile Treaty.
Political obstacles aside, building a missile defense involves daunting technical hurdles. Yet the Pentagon is trying to do it on a schedule that compresses 10 or 12 years' worth of work into just eight years.
One panel of experts warned that the fast-track schedule is likely to cause delays, increased costs, and even failure.
President Clinton will decide whether to go ahead with the planexpected to cost $60 billion by 2005after a crucial Pentagon technology test next month.
Some missile experts are urging the president to rethink the program.
Exclusive video obtained by CBS News shows a recent test of the systems ability to tell balloon decoyswhich an enemy missile would dispense them to confuse the missile systemand real warheads. In the test, the simulated warhead is deployed surrounded by decoys.
An expert says the tests demonstrate the "kill vehicles" that make up the missile shield can't tell bombs from balloons.
Theodore Postol, A Massachusetts Institute of Technology professor, has sent a letter to the White House warning that the kill vehicle "will be defeated by the simplest of balloon decoys."
Postol bases that devastating conclusion on data from a 1997 test in which an interceptor tried to pick out a warhead from a cluster of nine decoys.
"The kill vehicle cannot see any of these objects except as points of bright light," explained Postol. "It tries to tell whether it's looking at a warhead or a balloon and it turns out it can't be done."
A second missile expert, Dr. Richard Garwin, who reviewed the same data, concluded that, "the seeker on the kill vehicle really did not have any way to tell the warhead from the other objects that were there."
The Pentagon says Postol and Garwin simply haven't seen all the data, much of which is classified and points to a later test in which the kill vehicle distinguished between a balloon and a warhead and shot down the warhead.
"They went from 10 objects to two. One of them was the mock warhead and the other one was a 7-foot diameter balloon which was enormously bright, relative to the warhead," he said.
According to the Pentagon's own internal review of that test, the brightness of the decoy balloon did help the kill vehicle find the real target.
The test, the review concluded, "had significant limitations to operational realism."
The worth of the missile defense system will depend not just on what it can do, but what enemy missiles can do to elude it.
According to Postol, a North Korean ICBM with enough range to reach parts of the United States could be loaded with decoys that would confuse an American missile defense.
"There is no problem deploying a balloon. I mean, people build air bags for cars that are much more complicated than these balloons would be," Postol said.
Said Garwin: "It's a much easier task than making the ICBM in the first place."
But Garwin has nightmare scenario far worse than balloons: a missile loaded with small bombs filled with anthrax or some other deadly biological agent.
"It will release the bomblets which will spread over 10 or 20 miles as they fall to their target," said Garwin. "We won't be able to intercept hundreds of bomblets or probably even one."
Serious work on deploying a national missile defense began in 1996, and it is supposed to deployed in 2003.
According to the General Accounting Office, the NMD is supposed to combine early warning sensors on the ground an in space, tracking radar, a communications system and "ground-based interceptors to collide with and destroy incoming warheads."
The Anti-Ballistic Missile Treaty, or ABM treaty, was signed by the U.S. and Soviet Union in 1972 and limited the types of anti-missile systems the two countries could develop.
Under the treaty, the U.S. could only deploy a missile defense system at a single site around Grand Forks, North Dakota, and the Russians only around Moscow. The U.S.S.R. deployed such a system, but the U.S. has not.