The National Security Agency and its allies are making a final public push to retain as much of their controversial mass surveillance powers as they can, before President Barack Obama’s forthcoming announcement about the future scope of US surveillance.

Security officials concede a need for greater transparency and for adjustments to broad domestic intelligence collection, but argue that limiting the scope of such collection would put the country at greater risk of terrorist attacks.

In a lengthy interview that aired on Friday on National Public Radio (NPR), the NSA’s top civilian official, the outgoing deputy director John C Inglis, said that the agency would cautiously welcome a public advocate to argue for privacy interests before the secret court which oversees surveillance. Such a measure is being promoted by some of the agency’s strongest legislative critics.

Inglis also suggested that the so-called Fisa court have “somebody who would assist them with matters of interpreting technology”, which also has the potential to recast the court’s relationship with the NSA.

Currently, the judges on the panel rely entirely on the NSA to explain how the agency’s complex technological systems work, an institutional disadvantage that judges have highlighted in secret rulings bemoaning “systemic” misrepresentations by the powerful surveillance agency.

But security officials are arguing strongly against curtailing the substance of domestic surveillance activities.

While Inglis conceded in his NPR interview that at most one terrorist attack might have been foiled by NSA’s bulk collection of all American phone data – a case in San Diego that involved a money transfer from four men to al-Shabaab in Somalia – he described it as an “insurance policy” against future acts of terrorism.

“I'm not going to give that insurance policy up, because it's a necessary component to cover a seam that I can't otherwise cover,” Inglis said.

White House spokesman Jay Carney said Friday that Obama will unveil his surveillance proposals on January 17. Expectations are high that Obama will follow the recommendations of a review group he set up, which suggested that the responsibility for the bulk domestic call records database should be transferred from the NSA to a third party, such as the phone companies. But Inglis said that would not necessarily mean the end of the program, provided any dataset held outside of NSA had “sufficient depth” and “sufficient breadth” over “the whole haystack” of call records going back for years, and provided “sufficient agility” to the NSA to search it.

That is the subject of a heated dispute between the NSA and privacy advocates at the White House this week. Civil libertarian groups want to ensure that the legal standards for NSA to access phone records are heightened to prevent Americans not suspected of wrongdoing from being caught in surveillance dragnets, and that companies are not required to store data for longer than the 18-month average maximum in the industry.

On Thursday afternoon, a coalition of civil liberties groups met the White House counsel, Kathryn Ruemmler. Michelle Richardson of the American Civil Liberties Union, who was at the meeting, said the coalition’s main message to the White House was to end bulk domestic phone collection, rather than repackage it.

“Bulk collection is the big one, that’s the big question: whether you continue to spy on Americans or not,” Richardson said after the meeting. “You have to resolve that. That’s all people will remember.”

Inglis was bolstered on Thursday by the new FBI director James Comey, who said he opposed curbing the bureau’s power to collect information from businesses through a non-judicial subpoena called a national security letter. The use of national security letters, which occurs in secret, came under sharp criticism from Obama’s surveillance review panel, which advocated judicial approval over them.

Comey told reporters that would make it harder for his agency to investigate national security issues than conduct bank fraud investigations.

Surveillance skeptics who left meetings at the White House this week said they believe deliberations are still ongoing internally about how far back to scale US surveillance. Ron Wyden, the Oregon Democrat who sits on the Senate intelligence committee, told the Guardian on Thursday the “debate is clearly fluid”.

On Friday, Wyden and two intelligence committee colleagues, the Democrats Mark Udall and Martin Heinrich, released a letter to Obama in which they urged him to definitively end bulk surveillance on domestic phone data.

“While it might be more convenient for the NSA to collect phone records in bulk rather than directing individual queries to the various phone companies, convenience alone does not justify the collection of the personal information of millions of ordinary, innocent Americans, especially when the same or more information can be obtained in a timely manner using less intrusive methods,” the three senators wrote.

Obama’s White House staff were meeting representatives of tech firms on Friday, concluding a packed week packed of meetings with surveillance stakeholders.

Even as Inglis, who will soon retire, argued against the restriction of his agency’s powers, he said the burden will be on the NSA to be more forthcoming about what its activities actually are.

“We have to actually kind of be more transparent going forward, so the American public understands what we do, why we do it, how we do it,” he told NPR.