Washington - The national debate over US government surveillance, in a sharp and unexpected shift, seems to be turning in favour of reining in the National Security Agency's expansive spying powers at home and abroad.It's happened suddenly, over a span of just a few days. First, a federal judge ruled that the NSA's bulk collection of telephone records was unconstitutional, and then a presidential advisory panel recommended sweeping changes to the agency. Together, the developments are ratcheting up the pressure on US President Barack Obama to scale back the controversial surveillance programmes.Even Russian President Vladimir Putin chimed in on Thursday. He said US surveillance efforts are necessary to fight terrorism and "not a cause for repentance", but he, too, said they should be limited by clear rules.Obama is in no way obligated to make substantial changes. And, countering the public criticism he faces, he hears internal appeals from intelligence officials who insist the collection of phone and internet data is necessary to protect the US from terror attacks.Terror attacksBut even that argument has been undermined in the course of an extraordinary week. Federal Judge Richard Leon said in a ruling on Monday - its effect stayed, pending appeal - that even if the phone data collection is constitutional, there is little evidence that it has prevented terror attacks. The intelligence advisory panel, which had access to significant amounts of classified information and counted as a member a former acting director of the CIA, came to the same conclusion in its 300-page report.Democratic Senator Ron Wyden, a fierce critic of the NSA programmes, concluded: "What this says to the millions of Americans who have been concerned that the government knows who they called and when they called and for how long, this says it wasn't essential for preventing attacks."The White House has already rejected one proposal from the task force, which would have allowed for a civilian to head the NSA. While Obama spokesperson Jay Carney said on Thursday that the president was open to each of the panel's other 45 recommendations, a US official familiar with the deliberations said that Obama rejected a handful of the proposals out of hand when he met with the panel members this week.The president indicated he was comfortable with about half of the recommendations but thinks some others need further study, according to the official. That official commented only on condition of anonymity because the official was not authorised to discuss the process by name. Obama is expected to announce his decisions in January.Congress has been jarred by the new focus on government surveillance. For years, lawmakers had shown little interest in curtailing the programmes, but an unusual coalition of conservative Republicans and liberal Democrats has now taken up the issue.Modest changesHowever, Capitol Hill appears stuck over how to proceed. A broad bipartisan coalition in the House is backing legislation that would prohibit the NSA from collecting hundreds of millions of telephone records every day from US phone companies. But congressional leaders, who have been briefed for years on the classified terrorist-tracking programmes, generally support more modest changes to the surveillance systems and have sidelined the House measure.In the 12 years following the 11 September 2001 attacks, there has been no comparable large-scale terror incident in the US. The public has also learned much more about the government's surveillance activities, most recently in a wave of disclosures from former NSA contractor Edward Snowden."The further out we are from 9/11, the more the American public begins to ask the tough questions about the basics of liberties and civil rights," said Anthony Romero, the executive director of the American Civil Liberties Union. "The question for the president is whether he gets in front of the reform effort, shapes it, directs it and owns it, or whether he gets dragged along."NSA supporters worry that curtailing the surveillance programmes would leave the country vulnerable to threats.