The report, due to be discussed in federal parliament on Monday, but already comprehensively leaked, is expected to clear Australian politicians of "sexing-up" pre-Iraq war intelligence.
Instead of targeting politicians, the report is expected to criticise the quality of the advice spy agencies gave on the threat posed by former Iraqi president Saddam Hussein, according to leaks in local media.
The parliamentary joint committee on Australia's major spy networks, including ASIO and ASIS, was set up before US and British leaders decided under pressure to initiate inquiries into the quality and handling of pre-Iraq war intelligence.
But the Australian inquiry, headed by government backbench MP David Jull, was not able to look into new material that emerged after it stopped taking evidence.
This included crucial testimony by former US chief weapons inspector David Kay to a US committee in January that he did not think stockpiles of WMD existed. "It turns out that we were all wrong, probably in my judgment, and that is most disturbing," Kay said.
The question of why no evidence of a stockpile of chemical and biological weapons has been found since Australian troops were committed to the war in Iraq last March is also expected to remain unanswered by the Jull committee.
The Labour opposition has called for a royal commission-style inquiry, while the minor parties and independents who hold the balance of power in the upper house Senate, want a judicial investigation, along the lines of the inquiries ordered by US President George Bush and British Prime Minister Tony Blair.
Downer said the government would not object to a second inquiry although not one that was arranged for political reasons just before an election. Australia is expected to go to the polls in October or November.
"It turns out that we were all wrong, probably in my judgment, and that is most disturbing."
Former US chief weapons inspector
He said the Iraq Survey Group had not completed its investigation of the whole question of weapons of mass destruction, limiting the findings of the Jull committee.
"But look, if they decide to recommend a further inquiry and this is a bipartisan committee then my inclination would be to go along with that," he said.