Secretary of State Colin Powell said that the paper trail and interviews with Iraqis involved in the weapons programs would lead to the discovery of evidence.
Powell and Condoleezza Rice, the president's national security adviser, also flatly dismissed allegations that Vice President Dick Cheney applied political pressure to the Central Intelligence Agency to get intelligence officials to exaggerate their reports of the Iraqi threat.
British intelligence services were so alarmed by demands from Blair's government for evidence to justify an attack on Iraq that they kept careful files detailing all contacts with Blair's staff, London's Independent reports.
The spies are reportedly threatening to release the information if the Blair government tries to blame them for faulty intelligence.
As two British parliamentary committees prepare to investigate intelligence released by Prime Minister Tony Blair to justify the war on Iraq, Blair's closest advisor has reassured Britain's secret service that the government will take greater care in presenting intelligence dossiers to the public.
A Blair spokesman said Sunday that Communications chief Alastair Campbell had written to the head of the Secret Intelligence Service and "assured the (intelligence) agencies that far greater care would be taken in dealing with anything that might impact on their reputation or their work."
One dossier, titled "Iraq: Its Infrastructure of Concealment, Deception and Intimidation," which was published in January, included material copied from an American student's thesis which was posted on the Internet.
Another, published in September 2002, claimed Iraq could fire chemical or biological weapons within 45 minutes of Saddam Hussein giving an order to do so.
American and British troops in Iraq have failed to find weapons of mass destruction, after visiting more than 230 suspected sites during the past 11 weeks. The lack of hard evidence has put huge pressure on Washington and London since Saddam's alleged possession of banned weapons was the main U.S. and British justification for invading Iraq.
A retired U.S. intelligence official who served during the months before the war said Saturday the Bush administration distorted intelligence and presented conjecture as evidence to justify a U.S. invasion of Iraq. Greg Thielmann was director of the strategic, proliferation and military issues office in the State Department's Bureau of Intelligence and Research.
Vice Admiral Lowell Jacoby, director of the Defense Intelligence Agency, said Friday the agency had no hard evidence of Iraqi chemical weapons last fall but believed Iraq had a program in place to produce them.