The council could keep the aspirational target of achieving 70 per cent of that growth within the 2010 urban limit while being flexible about providing capacity for "greenfields" growth outside it in satellite towns of Warkworth and Pukekohe and other rural and coastal settlements.
But councillor Dick Quax said the council needed to do a finer analysis of the capacity of the existing limits to cater for demand or it would face serious legal challenges to the plan.
"We need to be less focused on ideology and more focused on the needs of Aucklanders and their wants.
"There is no evidence that there is capacity for 280,000 new dwellings within the metropolitan urban limit."
He said the council should be realistic and direct officers to tone down their estimates or examine the capacity of the whole urban core in more detail.
Deputy Mayor Penny Hulse said it was just a figure to give some idea of a target to aim at.
But she agreed with Mr Quax that the indicative figure might be tested by developers and work done to determine the true capacity as a base for the unitary plan.
Mrs Hulse said no one could expect an absolute figure over 30 years and estimates would be regularly reviewed.
"We have a huge amount of land currently zoned for development at Hobsonville and Massey North and elsewhere within the metropolitan urban limits ready to go."
The Property Council reserved its comment until it had seen the details of the recommendations put up for adoption by the full council on March 29.