Former government contractor Edward Snowden downloaded about 1.7 million intelligence files in the biggest theft of U.S. secrets in history, according to a Pentagon report described by members of Congress.

The Defense Department report concluded that Snowden’s disclosures last year could “gravely impact” U.S. national security and put members of the armed forces “in harm’s way,” Representative Mike Rogers, chairman of the House Intelligence Committee, said in a statement today.

“This report confirms my greatest fears – Snowden’s real acts of betrayal place America’s military men and women at greater risk,” Rogers, a Michigan Republican, said in the statement. “Snowden’s actions are likely to have lethal consequences for our troops in the field.”

The classified Pentagon report emerged as President Obama prepares to announce new limits as soon as next week on National Security Agency spying programs. The intelligence community assessment of what Snowden has is still under way, according to a U.S. intelligence official who requested anonymity to discuss the classified assessment.

American officials are concerned that material Snowden is suspected of downloading, while it hasn’t been made public yet, could be used to help identify U.S. intelligence agents even if they’re not named in the material he took.

“As a result of these disclosures, terrorists and their support networks, now have a better understanding of our collection methods and, make no mistake about it, they are taking countermeasures,” said Michael Birmingham, a spokesman for the U.S. Office of the Director of National Intelligence.

Global Backlash

The Pentagon report wasn’t released in full and described in a statement today by Rogers and Representative C.A. “Dutch” Ruppersberger of Maryland, the top Democrat on the Intelligence Committee.

Obama is responding to a domestic and international backlash over revelations the NSA spied on leaders including German Chancellor Angela Merkel, hacked into fiber-optic cables to get data from Google Inc. and Yahoo! Inc., and intercepted Americans’ communications without warrants. Most of the spying was exposed by Snowden, who has been charged with espionage and theft and is in Russia under temporary asylum.

The restrictions to be announced by Obama will include tighter rules for spying on foreign leaders, according to an administration official who described the proposal on condition of anonymity. The president is also expected to call for putting a privacy advocate on the secret court that oversees the NSA programs, and is considering limits on the government’s ability to collect and store phone records.

Fight Terrorism

With the proposal, the administration is seeking to rein in U.S. surveillance without sacrificing its ability to use electronic intelligence gathering to fight terrorism.

A White House panel reviewing U.S. surveillance programs recommended in a report last month the creation of new criteria for spying on foreign leaders, including determining whether electronic surveillance is necessary and whether there are other means to obtain the needed information.

Obama met today with several members of Congress at the White House to discuss the future of NSA surveillance and records retention. The president told lawmakers he plans to announce his decisions at the end of next week, Senator Charles Grassley of Iowa, the top Republican on the Judiciary Committee, said in an interview after the meeting.

Snowden and others who leak government secrets shouldn’t be considered heroic whistle-blowers, FBI Director James Comey said today.

“When you are talking about revealing the ways in which we track terrorists or the identities and locations of agents, I struggle to understand how you can apply hero whistle-blowing label to that kind of information,” Comey said.

Comey didn’t elaborate on Snowden’s disclosures because the contractor has been charged with a crime. FBI spokesman Michael Kortan said that the director was expressing a “broader concern” about the dangers associated with such leaks. Kortan declined to elaborate.