The CIA however has rejected charges.

The intelligence committee said the CIA had failed to challenge assessments made in 1998 of the threat from alleged Iraqi weapons of mass destruction.

The leaked letter comes as the UK and US governments are facing mounting questions over the evidence used to justify war.

The letter to the CIA -- written by the Republican chairman of the committee and its top-ranking Democrat -- first appeared on the Washington Post's website on Saturday.

In it, Porter Goss and Jane Harman said the CIA had relied on old intelligence dating back to 1998 along with "some new 'piecemeal' intelligence" when formulating its reports on Saddam Hussein's weapons programmes.

"The assessment that Iraq continued to pursue chemical and biological weapons remained constant and static over the past 10 years," the letter said.

The lawmakers cited weakness in intelligence from spies on the ground and said the government needed to develop better sources.

US intelligence was "fragmentary and sporadic" after UN weapons inspectors left Iraq in 1998, the letter said.

"These assessments and long-standing judgements were not challenged as a routine matter within the IC (Intelligence Community)," the lawmakers wrote in the letter that reflected their own views and not the full committee's opinion.

The criticism was dismissed as "absurd" by CIA spokesman Bill Harlow.

"The intelligence community stands fully behind its findings and judgements," he said.

"In the post-1998 time period the intelligence community launched an important and sustained effort to enhance our unilateral understanding of Iraq and its weapons of mass destruction programmes.

"From all of our disciplines, important gains were made."

The CIA said the intelligence committee had not yet taken the time to evaluate fully how its assessment was made.

Members of the committee have spent four months looking at 19 volumes of classified material used by the Bush administration to make its case for war.