TUCSON, Ariz. » The nation’s largest military contractors, facing federal budget cuts and the withdrawals from two wars, are turning their sights to the Mexican border in the hopes of collecting some of the billions of dollars expected to be spent on tighter security if immigration legislation becomes law.

Half a dozen major military contractors, including Raytheon, Lockheed Martin and General Dynamics, are preparing for an unusual desert showdown here this summer, demonstrating their military-grade radar and long-range camera systems in an effort to secure a Homeland Security Department contract worth as much as $1 billion.

Northrop Grumman, meanwhile, is pitching to Homeland Security officials an automated tracking device — first built for the Pentagon to find roadside bombs in Afghanistan — that could be mounted on aerial drones to find illegal border crossers. And General Atomics, which manufactures the reconnaissance drones, wants to double the size of the fleet under a recently awarded contract worth up to $443 million.

The military-style buildup at the border zone, which started in the Tucson area late in the Bush administration, would become all but mandatory under the bill pending before the Senate. It requires that within six months of enactment, Homeland Security submit a plan to achieve "effective control" and "persistent surveillance" of all of the more than 1,900-mile land border with Mexico, something never before accomplished.

For military contractors, that could be a real boon. "There are only so many missile systems and Apache attack helicopters you can sell," said Dennis L. Hoffman, an Arizona State University economics professor who has studied future potential markets for the defense industry. "This push toward border security fits very well with the need to create an ongoing stream of revenue."

Since 2005, the number of Border Patrol agents has doubled to 21,000, and the stretches protected by pedestrian or vehicle fencing have grown to 651 miles as of last year from 135. But there are still large swaths where people trying to enter the United States illegally have good odds of success, particularly in rural Texas. And with budget cutting in the past two years, money for surveillance equipment along the border has been pared back.

"The main gap in our ability to provide a more secure border at this point is technology," Mark S. Borkowski, the head of acquisitions for Homeland Security’s Customs and Border Protection, told participants at a border security industry conference in March.

Military contractors have not played a significant role in lobbying for the passage of the immigration legislation, which includes $4.5 billion to bolster border security over the next five years.

But teams of lobbyists, including former Sen. Alfonse M. D’Amato, a New York Republican, and Benjamin Abrams, a former top aide to Rep. Steny H. Hoyer, D-Md. and House minority whip, have already been pressing Homeland Security officials and lawmakers on behalf of their clients, efforts that have been backed up with millions of dollars of industry campaign contributions.

Homeland Security would have to decide, in consultation with Congress, how to divide the money — on long-range cameras, radar systems, mobile surveillance equipment, aircraft or lower-tech solutions like more border agents or physical fences — decisions that would determine how various contractors might fare.

"It has been a tough time for the industry: People have been laid off or furloughed," said James P. Creaghan, a lobbyist who represents a small Texas company, Personal Defense, which is trying to sell more night vision goggles to Homeland Security. "This could help out."

Northrop has won some important allies on Capitol Hill, including Sen. Thomas R. Carper, D-Del., the chairman of the Homeland Security and Governmental Affairs Committee, who is urging the department to invest more in Northrop’s drone-mounted surveillance system, called Vader. General Atomics, which D’Amato represents, has so much support in Congress that it has pressed Homeland Security in recent years to buy more Predator drones than the department has the personnel to operate, so they often sit unused, according to an agency audit.

The specific requirement in the legislation now before the Senate is that Homeland Security must install surveillance equipment or other measures that would allow it to apprehend or turn back 9 out of 10 people trying to illegally enter across all sectors of the southern land border. The department would be prohibited from moving ahead with the "pathway to citizenship" for immigrants already in the United States until this new security strategy is "substantially operational."

The bill is scheduled to be taken up for debate on the Senate floor next week, and certain Republicans have already drafted amendments that would make the requirement even more demanding, explicitly mandating that the 90 percent standard be achieved before the pathway to citizenship can proceed.

The Tucson area, for years the busiest crossing point for illegal immigrants, has served as the testing ground for the federal government’s high-technology border effort, although even senior Homeland Security officials acknowledge it got off to a poor start.

Boeing was selected back in 2006, when the last major push by Congress to rewrite the nation’s immigration laws was under way, to create a "virtual fence" that would use radar and video systems to identify and track incursions, information that would then be beamed to regional command centers and border agents in the field.

But the ground radar system at first kept shutting down because of faulty circuit breakers, audits found, while the towers installed for the mounting of radar and advanced long-range cameras swayed too much in the desert winds. Even rainstorms snarled things, creating countless false alerts.

"It should have been pretty simple," Borkowski said in a recent speech of the troubled $850 million project. "We weren’t frankly smart enough."

Critics say the government often is too fixated on high-technology solutions. C. Stewart Verdery Jr., a former Homeland Security official who now runs a lobbying firm, said federal officials should instead focus their limited resources on making it harder for illegal immigrants to work in the U.S., an approach that would serve as an effective deterrent.

"Where are you going to get the biggest bang for the buck?" Verdery said. "Enforcement of the workplace is probably the best area to invest more dollars."

But the technological solutions still have many advocates in Arizona, where Border Patrol officials contend that the equipment Boeing installed, despite its flaws, has fundamentally changed the cat-and-mouse game that plays out every day.

One recent afternoon, as the temperature in the Arizona desert hovered near 100 degrees, Border Patrol agents stationed inside a command center in Tucson were notified that a ground sensor had gone off.

The command center, built under the Boeing contract, resembles the set from the Hollywood movie "Minority Report," with Border Patrol agents sitting in front of banks of computer terminals and oversized screens that allow them to virtually fly over huge expanses of open desert 70 miles away.

Using his computer, one agent pointed the long-range, heat-seeking camera at the location where the sensor had gone off. Within seconds, black-and-white images of a group of men and women walking rapidly through the desert heat appeared on his screen.

"One, two, three, four, five," the agent called out, counting until he reached 15 people in the group. He also carefully scanned the images to see if any of the people were carrying large sacks, a sign of a possible drug delivery, or had any rifles or other weapons.

The Border Patrol radios lit up as he directed nearby agents on the ground to respond and called for backup from one of Customs and Border Protection’s helicopters based in Tucson.

"What you see today is like night and day compared to what we had," said Cmdr. Jeffrey Self of the Border Patrol, who oversees the Tucson region. The Boeing system, along with the surge in Border Patrol agents, has resulted in a major drop in attempted illegal crossings, he said, with apprehensions dropping 80 percent since their peak in 2000, considered a sign of a drop in overall traffic.

But the system’s weaknesses are still apparent. The computer terminal crashed while the search was underway, cutting off one agent’s video feed. And on that recent afternoon, no air support was immediately available. The one helicopter nearby that was on duty was running low on fuel, so it did not arrive on the scene until 90 minutes later.

Meanwhile, the Border Patrol agents at the Tucson command center lost the border crossers as they dropped into a ditch, taking them out of the line of sight of the camera and radar.

Apparently seeing Border Patrol trucks and the helicopter, the group realized it had been spotted and retreated back south, an agency spokesman said. The 15 were marked down as "turn backs."

Homeland Security has been preparing for more than a year to expand this system, under a new contract that would rely on proven surveillance technology. That is why the military contractors vying for the job will be asked in coming weeks to demonstrate their gear. The department also wants to identify a mix of equipment – some on fixed towers, others on trucks for mobility – so that officials can tailor uses to the different needs along the border.

Department officials said their choices would be driven by a determination of what the best available tools were for securing the border, not what the defense contractors or their lobbyists were pitching. Customs and Border Protection officials, said Michael J. Friel, a department spokesman in a statement, are "dedicated to continuing this progress towards a safer, stronger and more secure border."

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