Environmental groups have been fighting to protect swathes of native grasslands under threat from Defence Housing Australia's proposed redevelopment of the old Belconnen naval transmitting station near Lake Ginninderra.

Defence Housing Australia has already revised its plans in order to preserve a "significant" portion of the 144-hectare site from development.

But conservationists remain concerned, arguing the scaled-back plans merely shift the impact from one endangered grassland to another.

In the middle of the federal election campaign, candidates vying for the seat of Canberra have spoken out about their concerns.

The plans are expected to be submitted for federal environmental approval in the middle of this year, meaning the election campaign comes at a critical juncture for the project.

Greens candidate Tim Hollo this week told an ACT Conservation Council-hosted election forum that he would advocate for Defence Housing Australia to dump its plans if he was elected on May 21.

Mr Hollo used the controversial project to highlight the need for a wider shakeup of the planning system in Canberra, including the role of the National Capital Authority.

Labor incumbent Alicia Payne didn't attend the forum because she was as a household contact for COVID-19. Ms Payne later tested positive herself.

Her replacement at the forum, Maddy Northam, told the audience that Ms Payne had "pretty significant concerns" about the project.

Ms Northam, who is Katy Gallagher's running mate on Labor's senate ticket, said Ms Payne had spoken with conservation groups and sought briefings from Defence Housing Australia.

"We would be seeking a lot more information about how they could possibly be justifying this [development], if it's already been deemed a sensitive and unique area," she said.

"I think it's pretty safe to say we've got pretty significant concerns."

Ms Payne did not have anything further to add when contacted by The Canberra Times.

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Liberal candidate Slade Minson backed the revised plan for the site.

"The amended development will provide housing for Defence personnel, as well as homes for the open market which are much needed," he said.

ACT Conservation Council executive director Helen Oakey was pleased the election candidates were taking the issue seriously.

Ms Oakey urged the candidates to commit to concrete action if elected, including scrutinising planning and environmental approvals.

She also wanted a review of Defence Housing Australia's funding model, accusing it of operating akin to a property developer.

The estate is for defence families, but blocks will be sold off on the private market.

"The Canberra community is effectively paying for DHA's housing by losing areas of high environmental value," she said.

The organisation will turn up the pressure on the federal election candidates when they stage a rally near the Lawson site next Saturday.

In responses to questions from The Canberra Times, a Defence Housing Australia spokeswoman confirmed the project would be submitted for federal environmental approval in mid-2022.

"This project is currently in the planning and design stage and will seek to include a mix of traditional homes and medium-density living," she said

"Following extensive community consultation and feedback received in 2020, the draft masterplan has been revised to ensure that a significant portion of the 144-hectare site be preserved to minimise impacts to flora and fauna species, and ecological communities that exist on the site."