The Pentagon’s top missile defense official vigorously defended the system in a speech here Wednesday and compared the agency’s critics to some 20th Century skeptics who ended up being famously wrong in their predictions about the feasibility of earlier complex technologies.

In a March 20 speech during the 4th Annual U.S. Missile Defense Conference, which the agency co-sponsored with the American Institute of Aeronautics and Astronautics, Air Force Lt. Gen. Henry “Trey” Obering, director of the Missile Defense Agency (MDA), acknowledged that the Ground Based Midcourse Defense System has faced significant challenges, but he also compared the program to previous American efforts to develop aircraft, nuclear weapons and manned spacecraft.

Obering said that while those other complex technology efforts also faced skepticism, their critics were eventually proved wrong.

And despite the agency’s challenges, Obering said he is confident the Ground Based Midcourse Defense System could provide at least a limited defense against missiles from North Korea.

While interceptors failed to take off in consecutive tests in late 2004 and early 2005 , the basic technology for the system was proven by four successful intercepts in five attempts from 1999-2002 — and a successful flight test of the operational configuration of the booster rocket in 2003, Obering said.

During his presentation, Obering displayed a slide with quotes from a group he dubbed “The ‘Experts.’” It included quotes from 1901 when the U.S. Navy’s chief engineer described attempts to build aircraft as a wasted effort, and from 1945 when a top military advisor to the White House stated that an atomic bomb “will never go off.”

The Wright brothers flew their first airplane two years after Rear Adm. George Melville made his remarks, and the U.S. military dropped the first atomic bomb on Hiroshima months after William Daniel Leahy made his comments.

The slide also featured a quote from Lee DeForest, inventor of the electron tube, who said in 1957 that astronauts would never land on the Moon, “regardless of all future scientific advances.” Twelve years later Neil Armstrong and Buzz Aldrin walked on the Moon and safely returned to Earth.

Obering then displayed a slide with quotes from two of the most prominent critics of the Ground Based Midcourse Defense System, which is built by Boeing Missile Defense Systems of Arlington, Va.

Those quotes featured Philip Coyle, senior advisor at the Center for Defense Information, a Washington-based think tank, who has said the missile defense shield is “incredibly expensive, and it doesn’t work.”

The other quote was from Theodore Postol, a professor of science, technology and national security policy at the Massachusetts Institute of Technology, who said that the interceptors “cannot tell the difference between warheads and the simplest of balloon decoys. This means the national missile defense system can simply not work.”

In a March 22 interview, Coyle said that comparing his comments to those about previous inventions was unfair. Developing a national missile defense shield is not an impossible feat, but MDA has yet to demonstrate it has the capability to shoot down a missile that deploys the types of decoys that would likely be used in a real attack, and does not appear to be on a path towards doing so, Coyle said.

“I think what Gen. Obering is doing is blaming the mirror for the Missile Defense Agency’s poor image,” Coyle said. “The reason the Missile Defense Agency has a poor image is because it keeps breaking its promises.”

Coyle also took issue with Obering’s math, noting that agency had failed to intercept targets in five out of eight tests from 1999-2002, not four out of five as the general stated during his speech.

Rick Lehner, an MDA spokesman, acknowledged that Coyle was correct about the system’s success rate, but said that the agency did not count two of tests that included misses because the kill vehicle had failed to separate from the interceptor’s booster rocket.

Obering’s figures also addressed the fiscal years 1999-2002, which begin in October, and thus did not cover a December 2002 test that included a miss, Lehner said.

Postol did not return a phone call requesting comment by press time.

Obering acknowledged that the Ground Based Midcourse Defense System has had setbacks, and noted that MDA is behind its previous schedule for interceptor deployments. The agency had previously hoped to have 20 interceptors in silos at Fort Greely in Alaska and Vandenberg Air Force Base in California by now, but only has nine, he said.

However, the agency hopes to have a total of 22 interceptors in place by the end of 2007, and 38 by the end of 2009, Obering said. That number could grow to 50 interceptors by the end of 2011, 10 of which could be placed at a still to be determined European site, he said.