Former bosses of the Australian War Memorial will ask Parliament to block plans for a $500 million redevelopment of the historic site, warning its dignity is at risk of being overwhelmed.

Brendon Kelson and Steve Gower are among opponents of plans to increase the memorial's footprint by 80 per cent, with the former directors set to tell a parliamentary committee the federal funding allocated to the project should be redirected to veterans' services and other cultural institutions.