"That three-stage configuration could be capable of delivering small payloads to the United States," Walpole told CBS News National Security Correspondent David Martin.
Even before the North Korea test, the Pentagon was spending $3.5 billion dollars a year on developing a defense against missiles. The August tests, says Deputy Defense Secretary John Hamre have brought "Â…much more focus and urgency to this."
Iran is another country that recently rolled out a missile capable of hitting U.S. troops in Saudi Arabia, yet the Pentagon's attempt to develop a defense that can shoot down incoming missiles has been lurching from failure to failure.
"We haven't had any successes in the missile intercept tests," says Hamre. "That's a disappointment."
One particular missile is now 0 for 5 in intercept tests. Another missile -- a souped-up version of the Patriot used in the Persian Gulf War -- has yet to be tested, but already is projected to cost twice as much as it was supposed to.
One senior military officer told CBS News it is "insane" to be spending so much money and have so little to show for it. Yet Republicans in Congress have just added an extra $1 billion for missile defense despite this warning from Hamre.
"You couldn't give us more money to accelerate that, 'cause we just couldn't go any faster," Hamre says.
Shooting down an incoming missile traveling at speeds of to 12,000 mph is difficult but not impossible.
"We'll solve that, but that isn't the problem and never has been," says physicist Richard Garwin.
Garwin was a member of a blue ribbon panel that warned of the growing missile threat.
"There's a big threat out there, and not one that can be solved by a national missile defense," says Garwin.
As the CIA's Walpole points out, there are ways to deliver weapons of mass destruction that make missile defense irrelevant.
"An aircraft, a truck, some package left somewhere in a subway," Walpole begins. "Some of the countries [now] have the capability of doing those kinds of things with a chemical or a biological weapon."
This country survived the Cold War without a missile defense because the former Soviet Union could be counted on not to commit national suicide by starting a nuclear war. But what about North Korea?
Hamre fears the possibility of a foreign government in collapse deciding to launch as a last resort for its own survival. In such a worst-case-scenariono one knows if the anti-missile systems will work. But the U.S. has spent $50 billion over the last 15 years trying to make it work and is not about to give up now.
Reported By David Martin