DENVER -- Denver International Airport is being considered for a program in which unmanned spy planes could be used to thwart ground-based attacks on jetliners.

The Department of Homeland Security has chosen six airports of interest, including Denver; Los Angeles; Newark, N.J.; San Diego, Calif.; Las Vegas; and Washington, D.C.

This week, Homeland Security officials will receive proposals on such a project. Contracts could be awarded by August.

The idea is to zap shoulder-launched, heat-seeking missiles with a directed-energy weapon such as a high-powered laser or microwave system, or throw them off-course with low-energy lasers carried by aircraft like a modified, unmanned Predator, said John Pike, director of globalsecurity.org, a military information Web site.

"We are looking for other ways to further protect our aircraft, in particular our commercial aircraft," said Sue Mencer of Brownstein, Hyatt, Farber and Schreck in Denver. "They are either to be used for surveillance purposes to detect anything that might harm an aircraft, or indeed to actually be armed with laser-type technology that if any kind of a shoulder-held rocket were fired at an aircraft, it would detect and then deter and actually divert that hand-held device."

Mencer is the former Homeland Security director of the Office for Domestic Preparedness. She said the drones are an unfortunate necessity in this day and age.

"I think any kind of weaponry is available (to terrorists) if you know where to look and how to buy it whether it's on the open market or the black market," she added.

The Department of Homeland Security's Science and Technology Directorate expects to award at least one contract for the project, with about $11 million likely to be available for an unmanned aerial vehicle manufacturer.

"Any technology that enhances security is important to look at," said Mencer. Mencer pointed out that the Department of Homeland Security has considered equipping every commercial jet with a missile defense system, but that would be very costly.

Front-runners include General Atomics Aeronautical Systems Inc., producer of remotely piloted Predator spy planes, including the MQ-1 Predator, and its faster, higher-flying big brother, the MQ-9 Reaper.

"(These airports) are sort of representative of airports that industry would have to think about as we create systems,'' said Chris Kelly, Department of Homeland Security spokesman for science and technology. "This is kind of a setup where this unmanned aerial vehicle would have to fly over."

A Homeland Security Department announcement in late March described how countermeasure drones would loiter at more than 50,000 feet over an airport's approach and takeoff space and use high-tech equipment and cameras to spot heat-seeking missiles launched by "man-portable air defense systems."

The announcement said countermeasures must be designed to protect airspace "bounded by the threat envelope," defined as a three-mile radius around an aircraft operating at or below 18,000 feet in standard approach and departure corridors.

Kelly said testing might be done at a Navy range at Patuxent River, Md.

Las Vegas' McCarran International Airport, the sixth busiest airport in the United States, is on the list because of its concentration of passenger jet traffic. Aviation Department Deputy Director Rosemary Vassiliadis said her department generally supports efforts to develop technology to improve safety, but added the airport's priorities were elsewhere.

McCarran officials said no federal agency has contacted the Clark County Department of Aviation to discuss the anti-missile defense system, dubbed Project Chloe.

"At the moment, our primary concern in Washington remains in securing the necessary federal funding to ensure that a full complement of Transportation Security Administration screeners is available'' to handle the growing demand at the airport's checkpoints, she said.

Project Chloe evolved as Homeland Security's solution to the airline industry's reluctance to equip commercial jets with expensive, high-maintenance laser and missile detection systems.