WASHINGTON (Reuters) - New revelations from former security contractor Edward Snowden that U.S. intelligence agencies have access to a vast online tracking tool came to light on Wednesday, as lawmakers put the secret surveillance programs under greater scrutiny.

Antennas of Former National Security Agency (NSA) listening station are seen at the Teufelsberg hill (German for Devil's Mountain) in Berlin, June 30, 2013. REUTERS/Pawel Kopczynski

The Guardian, citing documents from Snowden, published National Security Agency training materials for the XKeyscore program, which the British newspaper described as the NSA’s widest-reaching system that covers “nearly everything a typical user does on the Internet.”

Intelligence analysts can conduct surveillance through XKeyscore by filling in an on-screen form giving only a “broad justification” for the search and no review by a court or NSA staff, the newspaper said.

Snowden’s disclosures to media that U.S. intelligence agencies collected data on phone calls and other communications of Americans and foreign citizens as a tool to fight terrorism have sparked uproar in the United States and abroad.

Intelligence officials insist the surveillance programs helped thwart terrorist attacks and saved many American lives.

“The implication that NSA’s collection is arbitrary and unconstrained is false,” the agency said in a statement in response to the Guardian’s new report, calling XKeyscore part of “NSA’s lawful foreign signals intelligence collection system.”

Opposition to the sweeping surveillance has been gaining traction in Congress, despite intense lobbying on the intelligence agencies’ behalf from the Obama administration, congressional leaders and members of the House of Representatives and Senate Intelligence Committees.

President Barack Obama scheduled a meeting for Thursday with Republican and Democratic lawmakers, including the leaders of the U.S. Senate and House of Representatives Intelligence Committees, to discuss programs under the Foreign Intelligence Surveillance Act, a White House official said on Wednesday.

Intelligence officials were grilled at a Senate Judiciary Committee hearing on Wednesday about their data gathering, the lack of transparency and security lapses that let Snowden get away with so much information.

SENATE, HOUSE LEGISLATION

Two Democratic members of the committee, Senators Al Franken and Richard Blumenthal, said they would introduce legislation on Thursday to force the Obama administration to provide more information about the data collection programs, including how many Americans’ records were reviewed by federal agents.

“The government has to give proper weight to both keeping America safe from terrorists and protecting Americans’ privacy,” Franken said.

Senior intelligence officials at the hearing said they were open to making some changes in the system.

Keith Alexander, the NSA director, jousted with hecklers at the Black Hat security conference in Las Vegas on Wednesday as he defended the U.S. spy agency’s surveillance programs before a crowd of cybersecurity experts and hackers.

“Read the Constitution!” one shouted. But the four-star general replied: “I have. So should you,” to sustained applause.

Last week, the House defeated by a narrow 217-205 margin a bill that would have cut funding of the NSA program that collects the phone records. Strong support for the measure - bolstered by an unlikely alliance of liberal Democrats and libertarian Republicans - surprised many observers.

Snowden, who has been charged under the U.S. Espionage Act and had his passport revoked, left Hong Kong more than a month ago and is stuck in limbo at a Moscow airport while seeking asylum in Russia, which has refused to extradite him.

“If a 29-year-old school dropout could come in and take out massive, massive amounts of data, it’s obvious there weren’t adequate controls,” Democratic Senator Patrick Leahy, the committee chairman, said at the hearing. “Has anybody been fired?”

John Inglis, the NSA’s deputy director, said no one had been dismissed and no one had offered to resign.

GOVERNMENT DECLASSIFIES DOCUMENTS

The director of national intelligence released three declassified documents on Wednesday in the “interest of increased transparency.” They explained the bulk collection of phone data - one of the secret programs revealed by Snowden.

Much of what is in the newly declassified documents has already been divulged in public hearings by intelligence officials. The released documents included 2009 and 2011 reports on the NSA’s “Bulk Collection Program,” carried out under the U.S. Patriot Act, the anti-terrorism legislation passed shortly after the September 11, 2001, attacks.

They also included an April 2013 order from the Foreign Intelligence Surveillance Court, which directed communications company Verizon to hand over data from millions of Americans’ telephone calls. The declassified documents said the data would only be used when needed for authorized searches.

“Although the programs collect a large amount of information, the vast majority of that information is never reviewed by anyone in the government, because the information is not responsive to the limited queries that are authorized for intelligence purposes,” the 2009 report said.

But the secret NSA slide show from 2008, posted by the Guardian on its website, showed that XKeyscore allowed analysts to access databases that collect and index online activity around the world, including searching for email addresses, extracted files, phone numbers or chat activity.