A multibillion-dollar project to hot-wire the new Southwest border fence with high-tech radar, cameras and satellite signals has been plagued with serious system failures and repeated delays and will probably not be completed for another seven years.

The system, originally intended to be completed next year, is still in the testing phase in two remote spots of the border in Arizona. There, the system combining sensor towers, communication relay systems and unattended ground sensors has been bogged down with radar clutter, blurred imagery on computer screens and satellite time lapses that often permit drug smugglers and undocumented workers to slip past U.S. law enforcement agents.

"It was a great idea, but it didn't work," said Mark Borkowski, executive director of the electronic fence program at the Homeland Security Department. "One of the kickers was that these radars had too many problems with clutter," Borkowski said. "Wind moving a tree shows up on the radar. And if you have too much of that, how do you find the person in the clutter? Same with cameras. The image is blurry."

He said that the U.S. government and its main contractor, Boeing Co., had made a series of mistakes since announcing in 2005 the plan to build sensor towers and radar scans alongside the new border fence. Although Borkowski said he remains hopeful the problems can be fixed, he cautioned that the technology ultimately might not cover the entire border. "It turned out to be a harder technological problem than we ever anticipated," Borkowski said. "We thought it would be very easy, and it wasn't."