The National Archives appeared before a Senate estimates committee late on Thursday evening to answer questions from government and opposition senators over its role to preserve important historical documents of the Commonwealth.

The archives' director David Fricker admitted to the committee thousands of documents would be permanently lost and many more were at risk as it grappled with a funding and resource shortfall.

The federal budget allocated an additional $700,000 to help address the issue in early May, falling well short of a recommendation by David Tune the agency needed $67.7 million to help save the records and reform the ageing system.

Labor senators asked Assistant Minister to the Attorney-General Senator Stoker why the agency had been the only cultural institution to be snubbed of a major funding increase.

She argued the government was considering its response to the Tune review's recommendations, adding it was to be expected that some records might be lost in the meantime.

"I don't think it's a risk you can ever completely reverse because time marches on and all sources degrade over time," Senator Stoker said on Thursday.

"The degradation of records over time is part of the ageing process, it's part of what the archives does."

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Earlier in the hearing, Mr Fricker added the records most at risk were stored on around 115,000 hours of magnetic tape.

Work was being done to triage and digitise the most important records, with Mr Fricker conceding it could not all be saved.

"It's unlikely we'll be able to preserve it all, so we are going to lose some of it," Mr Fricker said.

"It is in the archives because we have already appraised that as worthy of permanent preservation.

"We do have to do a significance assessment to see, well, among that collection ... of audio visual records, how are we going to prioritise ... what we are going to save and what will let potentially deteriorate beyond use?"

It comes a week after the archives made its plea to the public to donate in order to save the institution's degrading records.

It's offering 12-month memberships ranging between $20 and $80 and offering access to member-only events and behind-the-scenes tours.

Constitutional lawyer and researcher Professor Anne Twomey said the move wouldn't be enough to reach the needed multi-million-dollar target but it might signal to government its public value.

"Neither volunteering, nor public contributions will be sufficient," Prof Twomey said.

"But they might be a sign to the government that the institution is important, and the cause of protecting Australia's history is an important one."

Mr Fricker had earlier warned the loss of records had greater implications for democracy.

"The difference between the archive and other collecting institutions is an item is in the archives because it is unique, it's the one and only version - so if we lose records, that's permanently, irretrievably lost," he said in a March estimates hearing.

"The memory of a nation would be placed at risk."

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