This year, Congress has been all over the map on funding the Airborne Laser (ABL). The administration requested $549 million in the 2008 defense budget to complete work and prepare for a lethal demonstration against a ballistic missile in 2009. Congressional action began when the House Armed Services strategic forces subcommittee cut the request by $400 million, which would have killed the program.

The full committee revised that draconian step, but still cut a very deep $250 million. The Senate Armed Services Committee weighed in with a $200 million cut. These are unusually deep cuts, especially on a program that is achieving considerable success. The stated rationale is that the limited funds available for missile defense should go to systems now being deployed.

Getting missile defenses in the field is a top priority, but Congress must take care not to adversely affect what could be a quantum leap in new technology. Such deep cuts would cripple the program, cause the loss of laser experts from the only major laser weapon in development, and seriously disrupt the primary boost-phase defense effort.

In the end, House appropriators cut the ABL by only $50 million. But they also inexplicably added $145 million for the Kinetic Energy Interceptor, a second-choice boost-phase technology. Senate appropriators are expected to act in September.

For years, critics claimed missile defenses could not distinguish warheads from decoys and other penetration aids. The solution, they said, was to stop missiles in the first few minutes of flight, known as the boost phase, before warheads and decoys are released. The Missile Defense Agency is trying to meet that challenge with the Airborne Laser.

Eleven years ago the Air Force

announced the initial contract to develop an ABL, saying it held potential to “revolutionize aerial warfare in the 21st Century.” The effort grew out of the first Gulf War, when Iraq launched Scud missiles at U.S. forces and Israel. The Scuds broke up, making it difficult for Patriot PAC-2s to hit the warheads, though many still did.

Then there was the threat of chemical and biological agents dropped from missiles in small submunitions. A missile with such weapons must be stopped before they are released. Similarly, a missile carrying multiple warheads, decoys or other penetration aids is best stopped before anything is released. That means in the boost phase, and the ABL is the best option to do this.

The challenge is to produce an interceptor with enough speed to strike a missile within a few seconds of launch, when flying slowest and burning brightest. Since nothing is faster than the speed of light, the Air Force turned to lasers on an airborne platform.

The ABL must locate a moving target, generate a powerful beam, send it a long distance, and hold it on target long enough to cause it to rupture.

A laser that can generate that kind of energy is huge, so

a major challenge was to reduce the laser’s size and weight to fit in a 747 aircraft. That goal has been accomplished.

Another challenge was to develop beam and fire control systems that could find, track and target moving missiles. In addition to the high-energy laser, the ABL aircraft carries two other lasers and six infrared sensors to detect and track targets. The beam control is the most sophisticated optical system ever built. These very complex technologies have been in development and testing for a decade, and are showing real progress.

A surrogate low-power laser currently is substituting for the high-energy laser during tests. In July, the ABL used its infrared sensors and beam control to find and track Big Crow, a modified C-135 aircraft. Another flight test put both tracking and surrogate lasers on target after compensating for atmospheric distortion. Cameras on Big Crow showed all laser beams hitting their targets, successfully demonstrating the entire engagement sequence.

More flight tests are being conducted, and later this year the high-energy laser will be installed in the aircraft. The program now is just two years away from demonstrating that it can hit and destroy a missile in the boost phase. Nearly all the hardware has been built and most of the cost has been paid.

It is important to finish testing this advanced technology to find out whether high-energy lasers will be practical weapons in future warfare. An Airborne Laser patrolling near Iran could defend U.S. bases in the Middle East as well as Israel and other allies. And ABLs flying over the Western Pacific could protect U.S. bases in the area, in addition to our allies in Japan, South Korea and Taiwan.

In a letter to Congress last month, U.S. Army Gen. B.B. Bell, commander of U.S. Forces Korea, noted that North Korea has some 800 ballistic missiles able to carry conventional and chemical weapons. Intercepting them in the boost phase “would be a huge combat multiplier,” he wrote. Gen. Bell urged Congress to restore funding for the ABL test program.

Congress should follow Gen. Bell’s advice and provide the funds needed to finish testing this revolutionary weapon system.

James Hackett is a former national security official who now lives in Carlsbad, Calif.