What is more, Washington knows “disturbingly little” about the atomic programmes of hostile states, even though the nuclear quests of Iran and North Korea are dominating US foreign policy.

“In some cases it knows less now than it did five or ten years ago,” the report said.

And agencies such as the CIA, the FBI and the Homeland Security department have continued to regard each other as rivals, rather than comrades.

President Bush welcomed the “sharp critique” and vowed to act on its “thoughtful and extremely significant” recommendations.

The commission’s panel of judges, lawmakers and academics, past and present, appointed by Mr Bush, had virtually no criticism of the way the Bush Administration had handled the Iraq intelligence, absolving them of virtually all blame.

It said the mistaken belief that Saddam was pursuing nuclear weapons was deeply embedded in the US intelligence community and was not the result of hurried work in the febrile atmosphere of 2002.

Moreover, the CIA had failed to pass on to policymakers new information that it received casting serious doubt on one of their key sources on Iraq’s weapons of mass destruction (WMD).

In particular, they did not communicate doubts about the evidence provided by a source codenamed “Curveball”, upon whom much of the assessment of Saddam’s supposed biological arsenal rested.

This was despite the efforts of Colin Powell, the former Secretary of State, to strip every piece of dubious information from the US case before he made his now infamous prewar address to the UN Security Council. General Powell said this week that he was “furious and angry” about the mistakes made over Iraq’s WMD.

“In this instance, once again, the intelligence community failed to give policymakers a full understanding of the frailties of the intelligence on which they were relying,” the report said.

The panel went a long way towards exonerating Dick Cheney, the Vice-President, and the hawkish civilians appointed by Mr Bush to run the Pentagon under Donald Rumsfeld, the Defence Secretary.

They have been widely blamed for exerting undue pressure on intelligence analysts to emerge with conclusions to fit the Administration’s view.

But the report said that the intelligence agencies, led by the CIA, collected “precious little intelligence for the analysts to analyse, and much of what they did collect was either worthless or misleading”.

The intelligence community failed to caution the White House and the Pentagon “just how little good intelligence it had — or how much its assessments were driven by assumptions and inferences rather than concrete evidence”.

The report said: “The analysts who worked Iraqi weapons issues universally agreed that in no instance did political pressure cause them to skew or alter any of their analytical judgments. That said, it is hard to deny the conclusion that intelligence analysts worked in an environment that did not encourage scepticism about the conventional wisdom.”

The panel — the Commission on the Intelligence Capabilities of the United States Regarding Weapons of Mass Destruction — was set up by Mr Bush last year to learn the lessons of the flawed WMD case against Iraq.

It was led by Laurence Silberman, a senior circuit judge and former Reagan Administration official, and Charles Robb, a former Democrat governor and senator from Virginia.

The nine-man commission included John McCain, the independent-minded Republican Senator and national security hawk. It spent a year conducting hearings in secret.

The report did praise intelligence agencies for Libya’s decision to end its pursuit of WMD, and in unravelling the network of A.Q. Khan, the father of Pakistan’s nuclear bomb.

• Sandy Berger, the National Security Adviser under President Clinton, will plead guilty today to taking classified documents about the Clinton Administration’s record on al-Qaeda from the National Archives.

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