FORT HUACHUCA, Ariz. - The Border Patrol launched Friday its unmanned drones that use thermal and night-vision equipment to help agents spot illegal immigrants trying to cross the desert into the United States.

The stepped-up surveillance is part of a mission that officials hope will stem the tide of illegal immigrants that have made Arizona the busiest illegal entry point along the 2,000-mile border with Mexico.

But the Department of Homeland Security, which is funding the program, also has plans to test the drones in northern states, over the Great Lakes and in Puerto Rico following the Arizona use, said Robert Smith, head of the Customs and Border Protection's unmanned aerial drone program.

The exact location and timing of those tests has not yet been determined, he said Friday.

The two Hermes 450 drones being used in the Arizona project can detect movement from 15 miles up, read a license plate, view a vehicle's occupants, and even detect weapons, officials said.

"This has great potential to assist us in ways that have never been possible before," said Michael Nicely, interim chief of the Tucson sector of the Border Patrol. The Tucson sector covers most of Arizona's border with Mexico.

Both drones were expected to go into regular use on Monday. They will fly 56 hours a week and can be used over preprogrammed flight paths or be sent to check out specific destinations.

The drones weigh almost 1,000 pounds, have a 35-foot wingspan and can fly faster than 100 mph. They will patrol at 12,000 to 15,000 feet. They can stay aloft for 20 hours at a time.

On Friday, the waist-high gray drone bearing the Homeland Security Department's seal buzzed down a runway before patrolling the partly cloudy desert sky. It takes 12 to 18 people to operate and monitor the images sent back by the drones, officials said.

The overall cost of the mission is estimated at least at $10 million, with the government spending about $4 million on the drones.

The aircraft are a key element of the Department of Homeland Security's efforts to achieve "operational control" of the border in Arizona. The drones' mission ends Sept. 30. Tests in cold and tropical climates should be completed by Sept. 30, 2005, said Smith.

Border Patrol agents catch hundreds of thousands of illegal immigrants trying to cross Arizona's sprawling, cactus-covered deserts each year. The agency had recorded more than 330,000 apprehensions since Oct. 1 in the Border Patrol's Tucson sector, which covers most of the Arizona border.

Officials hope the drones will deter immigrants from crossing and will enable agents to better help those who are in distress.

But Kat Rodriguez, an organizer for the human rights group Coalicion de Derechos Humanos, said changing U.S. border policy rather than increasing patrols is key to protecting lives.

"It's like throwing an infant in a pool and then jumping in and saving it. You act like the hero in a situation you created," she said.

The Hermes 450s, which Israel uses to patrol its frontiers, join a number of unmanned aerial vehicles being used in the United States.

Remote-controlled planes help gather data for environmental studies and patrol Western skies on wildfire watch. In Alaska, the Coast Guard is also testing a drone this summer for fisheries patrols and other uses.

Drones called Predators have also been successful in U.S. military and CIA operations. Missiles fired from Predators have killed al-Qaida operatives in Afghanistan and Yemen.