WA Premier Mark McGowan has launched a $500,000 review of the state’s public sector.

A week after announcing a 40 per cent cut to the public sector in an effort to reduce 41 departments down to just 25, Mr McGowan says experts will spend five months investigating just what decisions are needed to achieve that goal.

Former New Zealand state services commissioner Iain Rennie will chair the review team, which also includes former Indigenous Land Corporation chief executive Michael Dillon and former UWA senior deputy vice chancellor Professor Margaret Seares AO.

Mr McGowan wants to save $750 million from the sector over four years.

“This review is all about creating more collaboration, making sure the Government works for more effectively, that service delivery is the focus and targeting unnecessary spending,” Mr McGowan said.

The review should hand down its findings in October.

“I have asked the review panel to identify practical ways to deliver services in a more efficient and financially sustainable way,” Mr McGowan said.

“There are far too many departments and agencies in WA, compared to the other states. It creates red tape, makes it difficult to access services and is a burden for taxpayers.

“We will ensure our Government is outcomes driven and consistently held to account.”

The Government has given no word on just how many jobs will be culled, or if the savings will be made through a wage freeze.

WA Opposition Leader Mike Nahan defended the public sector; something not often required of a Liberal.

He said the Government's plan to impose whole-of-government Key Performance Indicators would not work.

“Performance-based pay has been tried and tested in the state before, it didn't work for simple reasons,” he said.

“One is the minister sets policy, not the bureaucrat. You cannot hold public servants accountable for the decisions of ministers.

“Second, the KPIs were not an accurate measure of wages.

“In our system of government ... the buck stops with the minister, you can't contract it out and that is what Mark McGowan is trying to do.”

Community and Public Sector Union (CPSU) branch secretary Toni Walkington attacked the Opposition, not the Government.

“[Dr Nahan] failed while being treasurer to ensure that this state stayed in a buoyant economic circumstance,” Ms Walkington said.

“He's left a set of financial books that are in tatters, he imposed arbitrary cuts across the public service.”

Unions WA and CPSU welcomed the opportunity for public servants to be heard.

“We believe that the ... review will identify that the arbitrary cuts have resulted in perverse outcomes,” Ms Walkington said.

“Of course people are concerned about their future. Our members though want to have a modern, innovative public service.

“This is an opportunity to get things right.”

Dr Nahan said the CPSU boss “should resign”.

“She's paid for and employed by her members to represent them, and one of the biggest threats to their employment and wage levels is the McGowan Government…she is saying nothing,” he said.