By Richard CowanWASHINGTON (Reuters) - As Washington weighs new cybersecurity steps amid a public backlash over mass surveillance, U.S. tech companies warned President Barack Obama not to weaken increasingly sophisticated encryption systems designed to protect consumers' privacy.In a strongly worded letter to Obama on Monday, two industry associations for major software and hardware companies said, "We are opposed to any policy actions or measures that would undermine encryption as an available and effective tool."The Information Technology Industry Council and the Software and Information Industry Association, representing tech giants, including Apple Inc, Google Inc, Facebook Inc, IBM and Microsoft Corp, fired the latest salvo in what is shaping up to be a long fight over government access into smart phones and other digital devices.Obama administration officials, led by the FBI, have pushed the companies to find ways to let law enforcement bypass encryption to investigate illegal activities, including terrorism threats, but not weaken it so that criminals and computer hackers could penetrate the defenses.So far, however, the White House has not spelled out specific regulatory or legislative steps it might seek.View gallery Some cybersecurity experts are skeptical that Congress will take legislative action to expand the administration's powers anytime soon, noting recent lopsided votes in the House of Representatives to rein in surveillance.White House spokesman Josh Earnest, responding to Reuters' inquiries, said the administration "firmly supports the development and robust adoption of strong encryption."But he added there were concerns about "the use of encryption by terrorists and other criminals to conceal and enable crimes and other malicious activity."FBI'S INTENTIONS KEYKate Martin, director of the Center for National Security Studies, a civil liberties watchdog group, said, "The ultimate question is whether the FBI is going to seek legislation that would put limits on development of encryption tools."View gallery The Obama administration is in the midst of an internal debate on the matter. Martin said the recent naming of Ed Felten, a computer science and public affairs expert, as deputy U.S. chief technology officer was an indication that Obama "takes seriously the privacy concerns."But at the same time, she noted, "Technology, and especially the globalization of communications, has outpaced U.S. law."The debate over whether there should be limits on encryption should include the question of whether there should be limits on when the government can lawfully get access to people's private information, Martin said.The industry letter to Obama also was sent to FBI Director James Comey, Homeland Security Secretary Jeh Johnson, Attorney General Loretta Lynch and other Cabinet heads.Days earlier, the United States enacted legislation that will curtail the government's ability to scoop up huge volumes of data related to records of Americans' telephone calls.View gallery At the same time, Washington is being battered by computer hacks. Last week a massive breach was disclosed at the U.S. Office of Personnel Management, with records of up to 4 million current and former federal employees possibly compromised.An explosion in government surveillance was an outgrowth of the Sept. 11, 2001, attacks on the United States and was exposed by former National Security Agency contractor Edward Snowden.The industry groups noted that online commerce has flourished in part because consumers believed their payment information would be secure."Consumer trust in digital products and services is an essential component enabling continued economic growth of the online marketplace," the industry wrote."Accordingly, we urge you not to pursue any policy or proposal that would require or encourage companies to weaken these technologies, including the weakening of encryption or creating encryption 'work-arounds'."(Additional reporting by Roberta Rampton; Editing by Kevin Drawbaugh and Tom Brown)