Although the government has plans to extend the network of cameras, ground sensors and radars along most of the border, officials said they'll draw on lessons from the first two segments in southern Arizona as they contemplate if and where to build more sections and how fast to complete them.
The government estimated it would cost $6.7 billion to cover most of the Mexican border by 2014.
"We do want some time to look at whether or not that really does make the most sense," said Mark Borkowski, the government's director of the virtual fence project. "Is it really sensible to spend all that money? Or are there other more measured approaches? Maybe there are some places along the border that make sense, but maybe not the entire border."
As it now stands, once both southern Arizona sections are in operation along 53 miles (85 kilometers) of the border, the next step would be to authorize construction through the majority of the 375-mile (600-kilometer) border in Arizona, the nation's busiest gateway for immigrant smuggling and a major thoroughfare for marijuana smuggling.
By using cameras, ground sensors and radars mounted on a series of towers, the system allows a small number of dispatchers to track illegal border-crossers on a computer monitor. They'll be able to zoom in with cameras to see whether it's a person or animal moving, and decide whether the movement requires sending Border Patrol agents to the scene.
The virtual fence, developed as part of then-President George W. Bush's border security plan, is designed to add another layer of protection at the border, along with thousands of Border Patrol agents and 650 miles (1,050 kilometers) of real fences.
The government and the contractor building the virtual fence said they were making solid progress after a series of setbacks earlier in the project.
While a prototype virtual fence in southern Arizona has been in use for nearly two years, the first permanent 23-mile (37-kilometer) stretch along the Mexican border near Sasabe, Arizona, would be handed over to the Border Patrol in January for testing, if everything goes as planned. The government hopes to begin construction on a second 30-mile (48-kilometer) section south of Ajo, Arizona, once environmental clearances are finalized.
The project was criticized because of delays and the government's finding in 2008 that the 28-mile (45-kilometer) prototype fence didn't work properly. That prompted the government to withhold some payments to its contractor, Boeing Co. The prototype will be replaced by the first permanent segment.
As virtual fence construction continues, the Border Patrol continues to use older technology that has limitations.
Borkowski, who took over as the project's top leader months after the prototype came under criticism, said it would be easy to blame Boeing for the project's early failures, but much of the fault rests with the government.
The government left it up to Boeing to figure out what the government needed, and the Border Patrol — the end user — wasn't asked to be very involved at the beginning, Borkowski said.
"Unfortunately, what we communicated was, 'We are going to put up a system, everybody is going to love it and when we turn it on, it will work right out of the box and the Border Patrol will be delighted.' And that's not what happened," Borkowski said.
Borkowski said he wasn't entirely satisfied with Boeing's work on the project, but that the company has shown improvements in recent months.
Tim Peters, a vice president for Boeing, said large, complex project experience fits and starts and that his company has made good progress in figuring how to tie together the project's off-the-shelf components.
"It's like sitting down at Christmas, and your kid or your nephew just got a box of Lincoln Logs, Legos and Tinker toys and now you have to figure out how to put those pieces together," Peters said. "And Legos don't necessarily play well with Tinker Toys, and Tinker Toys certainly don't play well with Lincoln Logs."
Ira Mehlman, a spokesman for the Federation for American Immigration Reform, which favors tougher immigration enforcement, said he wasn't confident that the virtual fence will end up being built along the whole length of the border and that the delays on the project show that the government wasn't serious about securing the border.
"The confidence will come when they actually have something out there that actually works and helps stop people from coming across the border," Mehlman said.