The announcement by Senator Carl Levin, ranking Democrat on the Senate Armed Services Committee, followed revelations that experts from the State Department had questioned CIA findings last month that two tractor-trailers discovered in Iraq were mobile biological weapons labs.

It also came after Committee Chairman John Warner rejected Levin's call for immediate bipartisan action stating, in a letter, that "the course of action for our committee should be to await the intelligence committee's findings."

"Accordingly, I have directed my Armed Services Committee staff to proceed and to keep Senator Warner, through his staff, informed on our work plan and to invite his staff to join with us at any time on any matter," Levin said in a statement.

He said he felt "a heavy responsibility" to look into "the objectivity and credibility of the intelligence concerning the presence of weapons of mass destruction in Iraq immediately before the war" and the effect of such intelligence on defense policy decisions.

The threat from Iraqi chemical and biological weapons -- as well as suspected efforts to build nuclear weapons -- was the US-British pretext for the March 20 allied invasion.

But more than two months since the fall of Baghdad, the US military and Central Intelligence Agency have found no such weapons, prompting speculation that in making its case for the war and getting Congress to authorize it, the administration had either used intelligence selectively, or pressured the intelligence community into turning a blind eye on questionable sources.

Critics cite a September 2002 Defense Intelligence Agency report, in which the DIA said there was "no reliable information" that Iraq was producing chemical weapons.

They insist the secret assessment was issued as Defense Secretary Donald Rumsfeld was telling Congress of Iraq's efforts to build up its chemical arsenal.

Vice President Richard Cheney, an ardent advocate of the war, paid repeated visits to CIA headquarters in the run-up to the conflict, a fact that made some wonder whether such attention put implicit pressure on agency analysts.

The intelligence committees of both the Senate and the House of Representatives are conducting separate closed-door reviews of the pre-war US intelligence.

But many Democrats believe their Republican colleagues are trying to artificially narrow the scope of the probe to shield the president from possible political fallout.

Democratic Congressman Dennis Kucinich has accused Republican leaders of the House intelligence committee of playing politics after the Republican-controlled House on Thursday defeated his amendment that would have ordered the CIA inspector general to conduct an audit of all telephone and electronic communications between the CIA and Cheney's office.

"My amendment sought information about the role the vice president may have played in causing the CIA to disseminate unreliable, raw, previously undisseminated, untrue information about Iraqs alleged threat to the US," Kucinich said in a statement. "This information must not be classified or protected by executive privilege."

Similarly, the House spurned a measure by California Democrat Barbara Lee that would have forced a review of intelligence shared by Washington with UN inspectors in advance of the war.

Lee warned after the vote that if the case of the war had been distorted, "then we severely undercut our ability to convince the world about future dangers from weapons of mass destruction in other countries."

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