National Security Agency Director General Keith Alexander is sworn on Capitol Hill in Washington, Thursday, Sept. 26, 2013, prior to testifying before the Senate Intelligence Committee hearing on the Foreign Intelligence Surveillance Act (FISA), and National Security Agency (NSA) call records. Clapper told lawmakers he's willing to consider limits on surveillance by the National Security Agency. Senate Intelligence Committee ChairmaSen. Dianne Feinstein, D-Calif., second from left, talks with from left, Deputy Attorney General James Cole, National Security Agency Director General Keith Alexander, and Director of National Intelligence James Clapper, on Capitol Hill in Washington, Thursday, Sept. 26, 2013, before the start of the committee's hearing on the Foreign Intelligence Surveillance Act (FISA), and National Security Agency (NSA) call records. Lawmakers who oversee US intelligence agencies are working to expand the government's spying powers to allow the FBI to immediately begin electronically monitoring terror suspects who travel to the United States and who already were under surveillance overseas by the NSA. From left, National Security Agency Director General Keith Alexander, Director of National Intelligence James Clapper, and Deputy Attorney General James Cole are sworn in on Capitol Hill in Washington, Thursday, Sept. Director of National Intelligence James Clapper testifies on Capitol Hill in Washington, Thursday, Sept. 26, 2013, before the Senate Intelligence Committee hearing on the Foreign Intelligence Surveillance Act (FISA), and National Security Agency (NSA) call records. Senate Intelligence Committee Vice Chairman Sen. Saxby Chambliss, R-Ga.,center, talks with Director of National Intelligence James Clapper, left, and Deputy Attorney General James Cole on Capitol Hill in Washington, Thursday, Sept. 26, 2013, prior to the start of the Senate Intelligence Committee hearing on the Foreign Intelligence Surveillance Act (FISA), and National Security Agency (NSA) call records. WASHINGTON (AP) - The nation's top intelligence official has sidestepped questions from a senator about whether the National Security Agency has tracked the whereabouts of millions of Americans using their cellphone signals. The testy exchange Thursday between NSA chief Keith Alexander and Democratic Sen. Ron Wyden of Oregon intimated that such tracking had taken place. Alexander says his agency can only collect such data with an individual court order. But he did not say whether the agency had ever collected information about locations from which cellphone calls are made. Wyden is a longtime critic of NSA surveillance methods. Earlier this year, he questioned Director of National Intelligence James Clapper about whether U.S. intelligence gathered the records of millions of Americans. Clapper said no, but had to apologize later when leaks by a former NSA systems analyst revealed the bulk collection of U.S. telephone records and email data. Lawmakers who oversee U.S. intelligence agencies say they'll work to limit the National Security Agency's use of U.S. phone and email records, while also broadening the government's spying powers to allow monitoring of terror suspects who travel to the U.S. after being tracked overseas by the NSA. Sen. Dianne Feinstein, D-Calif., chairwoman of the Senate Finance Committee, outlined proposed changes to the Foreign Intelligence Surveillance Act during a hearing Thursday. The law has come under fire by some in Congress after disclosures by Edward Snowden, a 29-year-old former systems analyst on contract to the NSA, stirred concerns among Americans that their civil liberties are being violated. Feinstein said legislation her committee is drafting would "strictly limit access to the... phone metadata records, expressly prohibit the collection of the content of phone calls," and limit the amount of time such U.S. phone call data could be kept. Such records show the date and length of calls, and the numbers dialed. She said the committee bill also will seek to broaden the government's ability to electronically monitor terror suspects who travel to the U.S. if they were already under surveillance overseas by the NSA. The aim of the new spying power is to close what lawmakers say is a surveillance gap between when a subject enters the U.S. - and the NSA stops spying on him - and when the FBI has built a case to permit its agents to begin following the target. Director of National Intelligence James Clapper told the committee he was willing to consider limiting both how U.S. telephone and email data collected by NSA is used, and the amount of time it is stored. He said he's also open to other proposed changes, like appointing an independent official to oppose the government in hearings before the Foreign Intelligence Surveillance Act court, the secret federal court that considers all government surveillance requests. Efforts to rein-in the once-secret surveillance programs have attracted an unusual coalition of liberal Democrats and libertarian Republicans, pitting them against House and Senate leaders who generally have expressed strong support for the NSA programs. Four senators unveiled legislation earlier this week to end the collection of millions of Americans' phone records and data on Internet usage. The legislation by three Democrats and one Republican would end longstanding NSA surveillance practices and open up some of the actions of the FISA court. Feinstein said her bill would change the part of the surveillance law that permits targeting of non-Americans outside the U.S. to allow uninterrupted spying on a suspect for "a limited period of time after the NSA learns the target has traveled to the United States, so the government may obtain a court order based on probable cause." NSA director Gen. Keith Alexander, one of the witnesses at Thursday's hearing, repeated his earlier contention that there's no evidence of intentional wrongdoing in any of the NSA spying programs, even though the agency has reported thousands of errors to the FISA court. Intelligence officials blame those errors on a system so complex that no single person at the NSA understood it. Alexander said there have been only 12 instances of "willful violations" of the laws governing the NSA - but none of those had anything to do with FISA. In a declassified internal report from 2012, NSA said nearly three-quarters of the 2,776 compliance incidents - those where NSA analysts made surveillance errors - involved suspects who had been under surveillance abroad before entering the U.S. legally or illegally. The NSA's mandate forbids it from spying on anyone inside the U.S., except in rare court-approved instances. In most cases, it falls to the FBI to track such suspects - and when the NSA calls to report a so-called roamer, it already has stopped surveillance. The FBI then has to decide quickly whether the person is dangerous enough to start following electronically, and if so, the agency has to scramble to build a case against the suspect. The FBI can ask the attorney general for emergency authority to track the target for seven days but then must win retroactive approval for the spying from the FISA court. "I call it the terrorist lottery loophole," where surveillance can be dropped for a matter of hours or days during the handoff between agencies, said Rep. Mike Rogers, the Republican chairman of the House Intelligence Committee, who also supports changing the law. "Bottom line is, there is a gap," said the senior Democrat on the committee, Rep. C.A. Dutch Ruppersberger. If in that gap period ... there's an attack that kills Americans ... shame on us all.