Western Australia has been stripped of its AAA credit rating by a global credit ratings agency which lowered its rating to AA+.

Ratings agency Standard and Poor's says the downgrade has occurred because of declining revenues and a blow-out in the state's debt.

It is the first time in more than a decade that WA has not had a AAA credit rating, and Premier Colin Barnett has conceded he bears some responsibility.

"What role did the government play in this downgrade?" he asked.

"The only thing I can say is maybe we're guilty of trying to do too much too quickly, maybe we need to slow down a little bit."

Mr Barnett has foreshadowed drastic budget measures to try to get the credit rating back up, including the potential sale of state assets.

"They call for fiscal responsibility so get ready because there's going to be a fair dose of it," he said.

"We're going to have expenditure cuts right across every area.

"Maybe some of the utilities, maybe some things that we don't need to do, maybe some areas of government activity that could be contracted out, as we've done in some areas, so expect to see a little more of that."

Election spendathon

Standard and Poor's Claire Curtin says WA's revenue has declined in the past 12 months.

"Revenues have been lower than expected, setting aside royalties, and expenditure has been higher so the state's operating performance has been weaker than we expected a year ago," she said.

And, she says the government has not done enough to combat climbing debt levels.

"There are structural budgetary issues that aren't being sufficiently addressed," she said.

WA's debt is predicted to rise to $22 billion over the 2013/14 financial year but it will be more than $28 billion by the 2016/17 financial year.

This will be a sevenfold increase from 2008 when the debt level was $3.6 billion.

WA's Treasurer Troy Buswell has conceded much more needs to be done, and the government may be forced to reconsider its infrastructure promises.

"We're not going to dig our head in the sand, and walk away from our responsibilities," he said.

"We have to do more to live within our means, we simply have to do more to protect the long-term sustainability of the state's finances."

Mr Buswell also flagged the sale of state assets to combat mounting debt.

Standard and Poor's said while the state budget was on the right path, it believed there was limited political will to implement it as there had already been some revising of the budget revenue and expenditure.

The WA Chamber of Commerce and Industry's chief economist John Nicolaou says the Government should have seen the ratings downgrade coming.

"I think the election campaign became an infrastructure spendathon," he said.

"I think we now need to look at all the infrastructure commitments that the government has made as part of the election campaign and assess whether they are providing value for money in the current budgetary environment."

Mr Nicolaou has called for projects such as the MAX light rail network and the airport rail line to be reconsidered, and he is backing the idea of asset sales.

"I think asset sales are certainly part of the solution to addressing debt levels," he said.

"What asset sales do is help to reduce the level of debt but they don't address the long term sustainability of government finances."

Stable economy

Ms Curtin said WA's economy is, however, likely to be stable.

"[This] reflects our view that the Government will implement enough of its fiscal action plan to ensure its cash operating balance remains positive," she said.

She says this could come under pressure.

"The rating could be pressured if WA's consolidated cash operating balance looked likely to fall into deficit without a convincing plan to return to surplus," she said.

"A cash operating deficit could be a result of revenue pressures, or from a failure to remain committed to sufficient cost-savings.

"An expectation that debt levels looked likely to breach 120 per cent of consolidated revenues would also likely pressure the rating."

The agency is not predicting a return to WA's AAA rating within the next two years.