WASHINGTON — While ballistic missile defense is still a work in progress, the U.S. Army has already quietly demonstrated that it can reliably shoot down small rockets and artillery rounds with a high-powered laser.

The technology is so promising the Army and the Israeli government are jointly spending $500 million to put the Theater High Energy Laser (THEL) on a truck and make it mobile (MTHEL).

Army officials and contractors are quick to point out the limitations of the technology — it is a short-range, ground-based system designed as a last-ditch defense against relatively small ballistic missiles — Russian Katyusha rockets in particular. Still, it is viewed as a bright spot in the development of missile defenses even by some of those usually critical of a U.S. missile defense effort.

Since June 2000, the laser has knocked down 25 Katyusha rockets and five 152 millimeter artillery cannon rounds at White Sands Missile Range in New Mexico. "It’s an important technical achievement," said Phil Coyle, a missile defense critic at the Center for Defense Information here.

Recovered rocket pieces show clean holes punched through the casings as if by a large-caliber bullet. But rather than using kinetic energy to destroy the target, the system uses concentrated light.

Contractor Northrop Grumman won’t say exactly how powerful the laser is, but it is under 30 megawatts, according to program manager Joe Shwartz. One megawatt equals one million watts of power. If converted into electricity, a megawatt will power roughly 500 homes for a year.

The THEL is powered by combining two gases — nitrogen trifluoride and ethylene — which creates the lasing medium deuterium fluoride.

"The beauty of the laser is that all the energy comes from a chemical reaction," said Shwartz, who adds the combination is very similar to a rocket engine that mixes fuel and an oxidizer to achieve thrust.

The platform presently sits in several large buildings at White Sands. The challenge is to shrink the chemical power generator, the beam director and computer controller down so they can fit into two trucks. Shwartz said the goal is to make the system simple enough for a two-person crew to both move and operate it.

DeFatta says one prototype MTHEL will be built in the 2007 to 2009 timeframe. The present program employs about 60 full-time workers.

The system has top military brass excited because there is currently no protection against the devastation of short-range rockets and artillery shells. If soldiers get any advanced warning at all, hiding in a bunker or lying face down and praying to the deity of choice is the only strategy for survival.

"There is no other capability right now," said DeFatta. "This gives us a potential curtain [of defense]."

Neither Northrop Grumman nor the Army will disclose the range of the laser system, but a Katyusha rocket can fly between 20 and 40 kilometers. Shwartz said his company is currently working to "expand the envelope of engagement" but the platform is not designed for longer range, heavier targets.

Range is always a challenge for laser weapons, said CDI’s Coyle, because distortions in the atmosphere tend to break up the beam of light. Northrop Grumman is also the prime contractor for the Airborne Laser, a megawatt-class system that it plans to fly in a modified 747. That platform is designed to get the laser closer to where intercontinental enemy rockets take off and shoot them down in their boost phase.

But putting a massive chemical laser in an airplane has proven technically difficult and the ABL program is both behind schedule and over budget.