WASHINGTON » National Security Agency chief Gen. Keith Alexander revealed today that his spy agency once tested whether it could track Americans’ cellphone locations, in addition to its practice of sweeping broad information about calls made.

Alexander and Director of National Intelligence James Clapper testified at a Senate Judiciary Committee hearing on proposed reforms to the NSA’s surveillance of phone and internet usage around the world, exposed in June by former NSA analyst Edward Snowden. But neither spy chief discussed proposed reforms; instead they were questioned about new potential abuses that have come to light since then.

Alexander denied a New York Times report published Saturday that said NSA searched social networks of Americans searching for foreign terror connections, and detailed 12 previously revealed cases of abuse by NSA employees who used the network for unsanctioned missions like spying on a spouse. He said all employees were caught and most were disciplined.

Alexander and Clapper also told lawmakers that the government shutdown that began Tuesday over a budget impasse is seriously damaging the intelligence community’s ability to guard against threats. They said they’re keeping counterterrorism staff at work as well as those providing intelligence to troops in Afghanistan, but that some 70 percent of the civilian workforce has been furloughed. Any details on the jobs held by the furloughed employees is classified.

Congress is mulling changes to the Foreign Intelligence Surveillance Act that some believe allows the NSA too much freedom in gathering U.S. data as part of spying on targets overseas.

Alexander told the committee that his agency once tested, in 2010 and 2011, whether it could track Americans’ cellphone locations, but he says the NSA does not use that capability, leaving that to the FBI to build a criminal or foreign intelligence case against a suspect and track him.

"This may be something that is a future requirement for the country but it is not right now because when we identify a number, we give it to the FBI," Alexander said. "When they get their probable cause, they can get the locational data."

He said if the NSA thought it needed to track someone that way, it would go back to the Foreign Intelligence Surveillance Court — the secret court that authorizes its spying missions — for approval. He added that his agency reported the tests to both House and Senate intelligence committees, and that the data was never used for intelligence analysis.

Only last week, Alexander refused to answer questions from Sen. Ron Wyden, D-Ore., about whether his agency had ever collected or planned to collect such "cell-site" data, as it is called, saying it was classified, but the general said the NSA released the information in letters to the House and Senate Intelligence Committees ahead of the Judiciary Committee meeting today.

Wyden was not satisfied with Alexander’s answer.

"After years of stonewalling on whether the government has ever tracked or planned to track the location of law abiding Americans through their cellphones, once again, the intelligence leadership has decided to leave most of the real story secret — even when the truth would not compromise national security," he said.

Alexander acknowledged his agency collects data from social networks and other commercial databases to hunt foreign terror suspects but is not using the information to build private files on Americans. He said the operations are only used in pursuing foreign agents and sweeping up information on Americans if they are connected to those suspects by phone calls or other data.

Alexander said that not all social network searches are authorized by the secret FISA court, but he added the agency’s searches are proper and audited internally. The authority flows from a presidential executive order on national security dating back to the Reagan administration in 1981, he said, adding: "It allows us to understand what the foreign nexus is."

Alexander called a recent New York Times report on the searches "inaccurate and wrong." The Times said the NSA was exploiting huge collections of personal data to create sophisticated graphs of some Americans’ social connections. The Times said the private data included Facebook posts and banking, flight, GPS location and voting records.

Alexander denied the NSA was building "dossiers," or personal files on Americans, even though the Times story never specifically suggested that was being done.

He said collecting such private metadata is "the most important way" to track a potential terrorist once they have been identified. He also said Americans are only directly targeted by such searches when they are under investigation for possible terror ties or they are the targets of terror activities. He added that suspected terrorists operating inside the U.S. could also be targeted under those private data searches.

As for the incidents when NSA analysts did abuse their spying powers, Alexander told senators none of them involved the programs that collect American telephone records or email data.

"Nine of those were abroad," he said. "Three were (in the U.S.) but involved persons abroad on two of those. And one was on a spouse or girlfriend."

The NSA’s inspector general detailed the violation in a letter to Congress that was released last week. Several cases clearly showed government officials using the surveillance system to probe for information about spouses or partners. In one case, an internal investigation found that the official had made internal surveillance queries on the phones of nine foreign women, including his girlfriend, without authorization and had at times listened in on some phone conversations. The same official also collected data on a U.S. person’s phone.

Alexander said all had been disciplined, and had retired, resigned or been reprimanded, except for one where there wasn’t enough evidence to prove wrongdoing.

Both Alexander and Clapper spoke of reduced capability of their workforce during the government shutdown. Clapper said he has tried to keep on enough employees to guard against "imminent threats to life or property," but may have to call more back to work if the shutdown continues.

"The danger here… will accumulate over time. The damage will be insidious," Clapper said. Clapper even raised the specter of treason, saying financial stress could make his intelligence officers vulnerable to being bought off by foreign spies.

The federal government effectively shut down as of midnight Tuesday because of a standoff over the federal budget.