One of the leading civil liberties supporters in the US Senate has said the Obama administration is considering scaling back its bulk collection of Americans' phone records.

Ron Wyden, Democrat of Oregon and a member of the Senate intelligence committee, told the New York Times that he believed the administration was increasingly concerned about the privacy implications raised by a surveillance effort it has performed for four and a half years, after National Security Agency whistleblower Edward Snowden revealed it to the Guardian.

"I have a feeling that the administration is getting concerned about the bulk phone records collection, and that they are thinking about whether to move administratively to stop it," Wyden told the Times.

Aides to Wyden said on Friday that the statement was based on public comments from executive branch officials and the senator's prior experience with the termination of a bulk email collection program in 2011, something the Guardian recently reported. The administration has given Wyden no additional assurances of changes to the phone records collection, the aides said.

A test of the administration's intentions about the future of the phone records collection is fast approaching. An order by the secretive Foreign Intelligence Surveillance (Fisa) court compelling Verizon to provide the NSA with records of customers' phone calls expires on 19 July. The secret surveillance court orders have been renewed every 90 days for years.

Yet it is unclear if the public will know whether the bulk collection will continue as it is, be modified, or be cancelled. Fisa court orders are not public documents.

It is also unclear when the Fisa court orders on other telecommunications companies expire.

Representatives from the White House, NSA, Justice Department and the Office of the Director of National Intelligence did not immediately reply to a request for comment.

Wyden, among the Senate's leading critics of the surveillance programs, has singled out the phone records collection as a violation of Americans' privacy. He and his Colorado Democratic colleague on the intelligence committee, Mark Udall, have challenged the Obama administration's claims that the phone records collection is vital to preventing terrorist attacks.

"We have not yet seen any evidence showing that the NSA's dragnet collection of Americans' phone records has produced any uniquely valuable intelligence," they said on 13 June.

Wyden and Udall were among 26 senators of both parties – a quarter of the US Senate – who wrote to James Clapper, the director of national intelligence, on 27 June to express concern about the bulk phone records collection. Those senators were concerned that the intelligence agencies might use the same legal provision cited for the phone records collection, Section 215 of the 2001 Patriot Act, to collect "information on credit card purchases, pharmacy records, library records, firearms sales records, financial information and a range of other sensitive subjects."