NCA chief planner Andrew Smith also told a Senate estimates hearings that the authority continued to have concerns over "the quality and character" of the proposed development of 1600 new dwellings in the area.

Mr Smith said he had submitted his latest letter to the ACT Land Development Agency in February or March.

"The first letter was last year, and the second letter by recollection was February or March.

"I had been told I was going to get [a response] a few weeks ago, and I'm now told I will get their letter in a few weeks time. And really, I'm waiting. But I have pushed," he said.

Mr Smith told the hearing the NCA was particularly concerned about the impact on Government House.

"It will significantly change the character of the approach to the Governor-General's residence and that is clearly something the NCA has an active interest in," he said.

The authority announced earlier that it would not support the development as proposed due to this issue, the impact on historic trees, and the plan for six-storey buildings near Dunrossil Drive.

Mr Smith also said the authority had met with the Yarralumla Residents Association, which has been critical of the parameters of the proposed development.

The NCA was grilled over whether it took the opportunity to give its views during the development of the proposal, so as to avoid the current face-off.

"There were opportunities and we did raise them. As the scheme was finalised there were a number of proposals that came into it, particularly around traffic management, that we were not aware of.

"It was only when we saw early sketch plans in March when the impact became clear," Mr Smith said.

Western Australia Labor senator Glenn Sterle, charged with questioning the NCA, also asked why the territory government was allowing more development at all.

"Isn't there enough units here in Canberra? Everywhere I go there is a crane, I don't know who is going to live in these joints," he said.