War Memorial director Brendan Nelson has told MPs the land, which appears to sit inside Remembrance Nature Park, would host buildings used by construction workers during the institution's redevelopment and later become a car park of 118 spaces.

Dr Nelson, speaking at a Senate estimates hearing on Wednesday night, said the memorial wanted to begin works on temporary buildings for construction teams late this year.

"The land that is immediately behind Treloar Crescent, behind the existing Anzac Hall, just across the road, we need to acquire that land. We don't anticipate this will be a problem, the ACT government has been very supportive with this project," he said.

"We want to acquire that land and build the facilities for the construction teams that will be coming in next year to work on the project."

This would prepare the nine-year, $498.7 million expansion of the War Memorial for a start late next year with the controversial demolition of the 17-year-old Anzac Hall, followed by work to rebuild it and extend the Bean building in early 2021.

Construction would start on an underground hall and entrance at the memorial's front in April 2021, and major works are expected to end in 2025, leaving gallery fit-outs as the next task.

"What's important in this is the galleries themselves need some effort," Dr Nelson said.

The War Memorial's plan to build behind Anzac Hall would push its boundaries beyond Treloar Crescent, which now divides its buildings from Remembrance Nature Park at the base of Mount Ainslie's popular walking track.

Previously-released artist impressions of the redeveloped memorial indicate a car park would sit in the nature park and adjacent to Treloar Crescent.

War Memorial assistant director of corporate services Leanne Patterson on Thursday said it intended to construct the car park but it would remain ACT land.

"There have been only preliminary discussions with the ACT government about the acquisition of land at the base of Mount Ainslie related to the memorial redevelopment project," she said.

"These discussions will continue as the project progresses."

The land behind the War Memorial is owned by the ACT government, but the National Capital Authority holds planning control over the site.

The NCA has not received a proposal regarding the use of the land for a potential car park or any other works.

An ACT government spokeswoman said Transport Canberra and City Services had preliminary discussions with the War Memorial about a location to store construction equipment and materials, as well as additional car parks.

"As discussions are relatively new, nothing has been determined at this stage," she said.

Dr Nelson earlier said the War Memorial would minimise the expansion's cost and length by breaking it into discrete projects contracted to different companies, which would complete works simultaneously.

The memorial will use a newly-built $16 million, 5500 m² storage space in Mitchell as a temporary exhibition area during the expansion, moving aircraft and other artefacts into the building from Anzac Hall before the demolition next year.

In a significant expansion of its exhibition and public space, the memorial will rebuild Anzac Hall over three levels, substantially grow exhibition space, and create a new entrance and research centre.

There'll be a complete redesign of the memorial's lower ground floor and a new underground exhibition hall to display large items such as helicopters and jet fighters, but the building’s original facade will remain unchanged.