"Logically, someone under NSA surveillance, such as a terrorist, may present more interest to the government if they are inside the United States," but the surveillance can be temporarily stopped while the NSA or FBI builds its case to permit uninterrupted spying, Feinstein said.
A congressional aide said the proposed legislation would not specify whether the NSA would be the agency that continues its surveillance or the FBI would be the agency that picks up the target. The aide was not authorized to be identified publicly and spoke on condition of anonymity.
Proposed changes to FISA are the subject of a Senate Intelligence Committee hearing scheduled Thursday. The nation's top intelligence officials, Director of National Intelligence James Clapper and Army Gen. Keith Alexander, the director of the NSA, were slated to testify.
The proposal seeking to close the surveillance gap has bipartisan support of the leaders of both House and Senate Intelligence committees.
"I call it the terrorist lottery loophole," said Rep. Mike Rogers, D-Mich., the chairman of the House Intelligence Committee. "If you can find your way from a foreign country where we have reasonable suspicion that you are ... a terrorist ... and get to the United States, under a current rule, they need to turn it off and do a complicated handoff" to the FBI.
"Bottom line is, there is a gap," said the ranking Democrat on the committee, Rep. C.A. Dutch Ruppersberger, D-Md.
"You have to get the evidence. The judge has to schedule a hearing and rule," Ruppersberger said, drawing on his own time as an FBI prosecutor building such wiretap cases. "If in that gap period, and there's an attack that kills Americans ... shame on us all."
Alexander has testified that there is no evidence of intentional wrongdoing in any of the NSA spying programs. Intelligence officials blame the thousands of errors the agency itself reported to the FISA court on a system so complex that, they have said, no single person at the NSA understood it. A compliance officer now tracks every keystroke the agency's analysts make.