Greens leader Bob Brown will today call for a senate inquiry into Australia's population.

Mr Brown said Prime Minister Kevin Rudd's vision of a "big Australia" with a population of 35 million by 2050 isn't sustainable.

"We live in a fantastic continent, privileged above all on the face of this planet," Senator Brown told reporters in Canberra on Sunday.

"It's going to take some very wise decision-making to keep it that way," he said.

"I'm saying definitively we do not have the infrastructure or plans for the infrastructure to carry 35 million people by 2050."

The Greens want an inquiry to investigate Australia's "carrying capacity" in terms of population impacts on infrastructure, the environment, health and education. It would report back by mid-2011.

Brisbane's Lord Mayor Campbell Newman raised the need for a national population policy on February 23 and repeated the call in front of Infrastructure Minister Anthony Albanese last week.

He also questioned whether the case had been made for a population of 35 million in Australia.

"Australia must have a national population policy to guide the debate about managing growth in its cities," Brisbane Lord Mayor Campbell Newman said.

He said the policy would set the framework for guiding investment decisions.

"I think all the [South-East Queensland] mayors have said very clearly - and we will be saying at Premier Bligh's growth summit - that there does need to be a national population policy," Cr Newman said.

The Lord Mayor said the federal government needed to make its case for an Australian population of 35.9 million.

"Let's have the debate, let's see why we need a population like that to support the taxbase to ensure that we can pay for people in their old age and hospitals," he said.

"But the case has not been made yet."

A population summit hosted by Premier Anna Bligh will be held in Brisbane on March 30-31.

Senator Brown said ignorance was preventing a rational debate about population growth.

"But there is a lot of ignorance which drives fear of discussing population because you'll be labelled 'racist'."

The Tasmanian senator did acknowledge, however, that calling for slower population growth would be popular.

"I've seen the polls, they don't want it (35 million by 2050)," he said.

"People are concerned about it. It's a debate I get all across the country."