The Bush administration faces a major test of its credibility from a Senate committee investigation into whether officials misused intelligence to make the case for a war on Iraq.

With US forces in Iraq unable to produce clear evidence of an active threat from Saddam Hussein's nuclear, chemical or biological weapons programs, the televised hearings will represent the most serious examination so far of how prewar statements on Iraq failed to live up to postwar reality.

The investigation could begin later this month, Senator John Warner, the Republican head of the the armed services committee, said.

Administration officials are embarking on new explanations for why US forces have been unable to find evidence of deadly weapons at known sites, amid growing public unease about recent statements from the Pentagon and CIA that Saddam's arsenal may never be found.

"People are challenging the credibility of the use of this intelligence, and particularly its use by the president, the secretaries of state and defense, the CIA director and others," Mr Warner told USA Today.

The investigation is expected to review public statements from senior officials about Saddam's weapons programs as well as the intelligence reports which formed the basis for their comments.

"If we don't find these weapons of mass destruction, it will represent a serious intelligence failure or the manipulation of that intelligence to keep the American people in the dark," said the Democratic senator Bob Graham, the former chairman of the intelligence panel and a presidential candidate.

That could prove uncomfortable for the defense secretary, Donald Rumsfeld, and the CIA director, George Tenet, who appeared before Mr Warner's committee in February, confident of finding evidence of Saddam's prohibited arsenal.

The Senate scrutiny will be seen as vindication by analysts at the CIA who have become increasingly public with their dismay at how their findings were projected by administration officials.

Washington received qualified backing in a report from Hans Blix, the chief UN weapons inspector, who said Iraq had not accounted for stocks of anthrax and had failed to declare what appeared to be mobile biological arms laboratories.

· The Australian defense minister, Robert Hill, has indicated that crucial intelligence information about Iraq's weapons of mass destruction may have been flawed.

"On the basis of what we understood, the action was the right action to take," Mr Hill told the Sydney Morning Herald. "If it turns out there were flaws in what we understood, then I think we ought to say there were flaws. But it's too early to say that."

© Guardian Newspapers Limited 2003

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