Privacy advocates pressed Barack Obama to end the bulk collection of Americans’ communications data at a series of meetings at the White House on Thursday, seizing their final chance to convince him of the need for meaningful reform of sweeping surveillance practices.

A key US senator left one meeting at the White House with the impression that President Obama has yet to decide on specific reforms. “The debate is clearly fluid,” senator Ron Wyden of Oregon, a longtime critic of bulk surveillance, told the Guardian after the meeting. “My sense is the president, and the administration, is wrestling with these issues,” Wyden said.

Other groups were meeting presidential aides on Thursday afternoon, including the representatives of the American Civil Liberties Union, the Electronic Privacy Information Center (Epic) and the Open Technology Institute. Expectations were mounting that Obama will propose changing the National Security Agency’s controversial database of all domestic phone call records.

“The White House must end the NSA bulk record collection activities,” said Alan Butler, a lawyer with Epic, voicing the bottom line of the civil liberties coalition.

Wyden, a member of the Senate intelligence committee, said he viewed the coming days and weeks, ahead of an announcement by Obama about the future scope of surveillance, to be decisive for the debate triggered by NSA whistleblower Edward Snowden.

“What I’d say to Americans is that the future of these programs is being determined now,” Wyden said. “For those like me, who believe that security and liberty are not mutually exclusive, this is the time to weigh in.”

During the “very detailed” White House meeting, Wyden said he pointed to findings from the recent report of Obama’s review group that the bulk collection of records of all phone calls made in the United States was “not essential to preventing attacks, and could readily have been obtained in a timely manner using conventional section 215 orders,” as the review group’s December report put it.

Advocates of bulk domestic phone data collection “need to make the case, and I don’t think they have,” Wyden said.

But in late December, a federal judge in New York, William Pauley, was compelled by government arguments that the bulk domestic collection of telephone records was a necessary counter-terrorism tool – a ruling that directly contradicted a different judge, Richard Leon; and gave the NSA a crucial lift for retaining its major domestic surveillance effort.

Advocates for curbing the NSA’s domestic phone data collection, who were scheduled to meet Thursday afternoon with Obama’s White House counsel, Kathryn Ruemmler, described the current surveillance debate as stalled and precarious, with crucial legislators paused in anticipation of Obama’s decisions, which he is expected to announce as early as next week.

One of the attendees at the meeting, Wisconsin Republican James Sensenbrenner – a co-sponsor of a pending bill to end bulk collection – said that legislative action would need to follow Obama’s impending speech.

“All three branches of government have said the NSA has gone too far,” Sensenbrenner said in a post-meeting statement.

Even President Obama’s hand-picked panel agrees that bulk collection by the NSA has come at a high cost to privacy without improving national security. This problem cannot be solved by presidential fiat. Congress needs to pass the USA Freedom Act, a bipartisan legislative solution closely aligned with the suggestions by the president’s panel. Enacting this bill would protect Americans’ civil liberties while keeping intact the tools necessary to protect our nation.

Speaking after the meeting with legislators, White House spokesman Jay Carney described the conversation as an opportunity for Obama to “solicit their input”, rather than brief them on his decisions about the future scope of surveillance activities.

The White House held meetings on Wednesday with the leadership of the intelligence agencies, including NSA director Keith Alexander and director of national intelligence James Clapper, as well as with Obama’s privacy and civil liberties advisory group. On Friday, Obama’s staff is expected to meet representatives of major technology firms, ostensibly to continue deliberations.

Shortly before the legislators’ meeting began, two of the attendees, House intelligence committee leaders Mike Rogers of Michigan and Dutch Ruppersberger of Maryland, issued a statement describing a classified Defense Department report that they said alleged that Snowden’s leaks –which they said totaled 1.7m intelligence files and impacted intelligence operations of all military branches – could “gravely impact” US national security.

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

Barack Obama recently met with technology executives at the White House to hear arguments about surveillance. Photograph: Evan Vucci /AP

A spokesman for the Defense Intelligence Agency, which spearheaded the report, said the report was an “initial assessment”, and the work of the Information Review Task Force was “ongoing”. But neither the House intelligence committee leaders nor the DIA would provide additional information substantiating the allegations of Snowden’s impact.

“The report is classified and is not releasable,” said the DIA spokesman, who would not agree to be quoted by name. The classified interim assessment was delivered to the House and Senate intelligence committees on 6 January, and the DIA spokesman said there is no deadline for a final report, nor a mandate to make such a report public.

Snowden's attorney, Ben Wizner, described the report as an attack on the journalism produced by the Snowden disclosures.

"In truth, Mike Rogers is only indirectly attacking Snowden. He’s directly attacking the journalists who have reported on these revelations. There is not a shred of evidence that any adversary has had any access to any document other than those published by journalists, and they haven't contradicted that," Wizner told the Guardian.

"We shouldn’t have any confidence in the accuracy of this innuendo. The government has shown time and again they have very little idea of what Snowden had access to."

But Snowden’s impact on the public debate about surveillance – which his disclosures to the Guardian and the Washington Post seven months ago kickstarted and transformed – is far more visible.

Speaking outside the White House after a separate meeting with Obama, senator Rand Paul also stepped up his calls for government leniency toward Snowden, contrasting his treatment with Clapper, who has admitted misleading the Senate about surveillance.

"Those who call for some sort of frontier justice for [Snowden] need to understand the laws needs to apply equally," Paul told reporters. "James Clapper by all accounts committed perjury which is punishable by five years in prison and if you want to throw the book at Snowden, it's a little hard to say 'Oh, but we're not going to do anything about James Clapper lying to Congress.'"

Asked if he was making a direct comparison, Paul added: "It's not my job to compare them or contrast what they did, but what James Clapper did has greatly harmed the credibility of the intelligence agencies ... he has really greatly damaged the intelligence community. It's arguable."

After meeting with Obama, Wyden saw the debate over surveillance winding toward a conclusion.

“This is crunch time. The decisions are going to be made in the very near future,” Wyden said.

“The president made clear he wanted to hear from us. I’m going to keep urging members of Congress and the public to stand on the side of real reform and end intrusive surveillance practices that in effect violate the liberties of our people without making us safer.”