Representative Bennie Thompson, Democrat of Mississippi and chairman of the committee, questioned whether it was time to pull the plug entirely.

“We still need to see whether or not this virtual fence that was promised by the department and its contractor Boeing is something that is feasible,” he said Tuesday. “Or is it just a several-hundred-million-dollar waste of taxpayer money?”

The virtual fence is part of a multiyear, multibillion-dollar effort known as the Secure Border Initiative that was announced with fanfare by the Bush administration in November 2005. Besides increasing the number of guards and expanding a border wall, it promised a sophisticated system of cameras, sensors and radar that would zero in on people crossing the border with new speed and clarity and quickly guide agents to them.

By now, according to the original timeline, the system was supposed to be working along the 2,000-mile border with Mexico. But shortly after Boeing was awarded the contract, red flags went up over its lack of oversight and potential for cost overruns.

Boeing said in a statement on Tuesday that it was “fully committed to delivering border-security technology that successfully assists” the department, but it declined to answer questions about its handling of the project. About $1.1 billion has been spent on the virtual fence, with little to show for it beyond the two testing sites in the Arizona desert and a series of embarrassments, including radar that could not function properly in the rain and wind-blown trees mistaken for border crossers.