Defence Housing Australia plans on building nearly 600 homes on the site of the former Belconnen Naval Transmitting Station in Lawson.

The site would be developed in two stages, and stage one already has development approval.

But more than 100 conservationists and ecologists signed a letter last month urging Defence Housing Australia to reconsider the development. The agency is yet to respond.

Conservation Council ACT executive director Helen Oakey said the site contained more than 100 hectares of natural temperate grassland.

Ms Oakey said the grasslands, one of around 13 similarly-sized sites remaining in the ACT and the last in Belconnen, were "critically-endangered ecological communities".

Less than 1 per cent of natural temperate grasslands remain across the country.

The grasslands are home to the critically-endangered golden sun moth and other rare insects like the Perunga grasshopper and Key's matchstick grasshopper.

It has the most extensive and most well-preserved kangaroo grass in the ACT and a population of the vulnerable striped legless lizard.

It also provides habitat for rare and vulnerable birds, including the superb parrot, scarlet robin and gang-gang cockatoo.

Ms Oakey said the destruction of this habitat was unacceptable, given Australia's biodiversity crisis.

"Right across Australia we have lost grassland sites because people didn't necessarily understand the ecological value that they had," Ms Oakey said.

"When you look at a grassland, sometimes you have to look a little bit deeper than just looking out over a vista to actually see what those ecological values are."

Friends of Grasslands president Geoffrey Robertson said while the ACT had done a better than other jurisdictions at preserving its grasslands, development had swallowed sites over the years.

"I don't know how far we can go before we've got nothing left," Mr Robertson said.

Mr Robertson said it would be a great shame if these grasslands were lost.

"I think very few people understand the biodiversity they have, and have no appreciation of them," Mr Robertson said.

"What is Australia for if not for its landscape and natural diversity?"

Defence Housing Australia was unable to respond to a request for comment by deadline.

The agency previously told The Canberra Times a "significant" portion of the site would be preserved for conservation purposes.

However Ms Oakey said site plans showed stage one of the project would impact the grasslands through what is known as an urban edge effect. Stage two built directly over grassland and box woodgum habitat.

Their push comes after recent analysis from the Australian Conservation Foundation found more than 20,000 hectares of threatened species habitat in the nation's 99 biggest cities has been cleared since the Environment Protection and Biodiversity Conservation Act was introduced.

Nearly 200 hectares of threatened species habitat had been destroyed in Canberra between 2000 and 2017.