Opposition parties in the Senate forced the conservative government of Prime Minister John Howard to set up the joint parliamentary hearing into the pre-war intelligence during an animated debate on Wednesday.

The move followed similar steps by the US Congress and British parliament amid reports their governments exaggerated the threat of Iraqi weapons of mass destruction to justify toppling Saddam Hussein.

Australia was the only other country to contribute forces to the Anglo-American invasion and Howard had steadfastly refused to order an inquiry into the pre-war intelligence.

His opponents, led by the Labor Party, finally succeeded Wednesday in pushing a vote through the opposition-controlled Senate to have a joint security committee made up of Senators and members of the lower house of parliament hold the hearings.

Howard assailed the move as "completely opportunistic and totally political".

But minor opposition parties were also critical because the joint security committee is controlled by Howard's conservative coalition and will hold its deliberations behind closed doors.

"In short, this will be a secret inquiry where the outcomes may or may not be reported to parliament," Senator John Cherry of the Democrats party said Thursday.

The Greens party complained that by focussing only on the issue of banned Iraqi weapons, the inquiry would not probe the "true reasons" US President George W. Bush pushed so hard to invade Iraq.

"Was it just weapons of mass destruction or was it the oil, the geopolitics, the Israeli question and other issues which were very, very important to the motivation of the White House in invading Iraq?" asked Greens leader Bob Brown.

"The intelligence agencies of Australia will have informed the government about that and I don't think we've seen what that evidence was," he said.

Other critics of the inquiry complained that the joint parliamentary committee, formed last year to oversee government intelligence activities, did not have the authority to question officials from two key agencies.

The committee only has the power to inquire into the domestic spy agency, ASIO, its foreign counterparty ASIS and the Defense Signals Directorate.

It cannot summon officials from the Office of National Assessments and the Defense Intelligence Organisation which are responsible for providing the bulk of intelligence reports on Iraq to the government.

Howard defended his decision to join the invasion of Iraq despite widespread domestic opposition as necessary to prevent the spread of chemical, biological and possibly nuclear weapons allegedly held by Iraq.

But since US-led forces toppled Saddam's regime in April, no stockpiles of banned weapons have been found.

Howard insisted Thursday that more time be given for inspectors to find the illegal arms.

"I believe that people should be more patient about the discovery of further evidence," he said in a radio interview.

"Any suggestion that we at an Australian government level, we asked the intelligence services to massage or overstate material is wrong and it is also very insulting to them," he said.

WAR.WIRE