The authority's boss Sally Barnes said it could make it clearer to the public what decisions it had the power to make, after it was inundated with objections to aspects of the memorial upgrade - including its $500 million price tag and purpose - which fell outside its remit.

The authority last week green-lit an application for early construction work on the highly contentious project, which includes demolishing the award-winning Anzac Hall to make for new gallery space.

The ruling, which was made on the grounds the project was not at odds with the National Capital Plan, came despite fierce and sustained public opposition.

The overwhelming majority of the 600 submissions to public consultation objected to the redevelopment, with dissenters criticizing the expansion - in particular the Anzac Hall demolition - as a waste of taxpayer funds which threatened to undermine the memorial's purpose as a place for solemn reflection.

Fronting a federal parliamentary committee on Thursday morning, Ms Barnes said questions about the project's cost, purpose and what would be housed inside the expanded memorial were outside the authority's "purview".

Those issues had already been canvassed, and the project backed, by parliament's public works committee, she said.

While the consultation website had explained that was the case, Ms Barnes said most submissions chose to comment on the issues anyway.

"They chose to comment on what we wouldn't be considering," she said.

"That is their prerogative and obviously they wanted to raise their issues regardless of whether it was stuff that we were considering."

Ms Barnes said during consultation on the next stage of the expansion the authority would make it "clearer" exactly what was being assessed.

"The next lot of consultation will be about construction work, and we won't be revisiting the purpose or the cost - that has been approved by the Australian parliament," she said.

"We won't be revisiting Anzac Hall coming down."

Ms Barnes said a recent audit of authority's consultation processes had found it was being handled properly.

But she was open to changes, including putting notices in national newspapers to alert a wider audience to consultation.

She noted the authority was able to rule on the proposed razing of 140 trees, which emerged as a significant concern among opponents.

The trees will be ripped up, however the memorial will be required to plant a further 240 mostly native trees, she said.

Meanwhile, Ms Barnes said the authority had been tasked with scouting options for a new cultural institution which would hold the repatriated ancestral remains of Indigenous Australians.

May's federal budget allocated $4.7 million in the next financial year for a detailed business case on the establishment of the so-called Ngurra Cultural Precinct.

Ms Barnes would not disclose which specific sites were under consideration, but said the proposed institution was deserving of "a very prominent and nationally significant place" within Canberra's parliamentary triangle.

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: