President Bush's claim three years ago that weapons of mass destruction were found in Iraq was based on U.S. intelligence that was later proved false, the White House acknowledged on Wednesday.

Presidential spokesman Scott McClellan vigorously denied suggestions that Bush was making claims that had been debunked when he said two small trailers seized in Iraq were mobile biological laboratories.

Bush declared in a May 2003 television interview, "We have found the weapons of mass destruction." The claim, repeated by top administration officials for months afterward, was cited at the time as supporting evidence for the decision to go to war.

The Washington Post reported Wednesday that experts on a Pentagon-sponsored mission who examined the trailers concluded that they had nothing to do with biological weapons and sent their findings to Washington in a classified report on May 27, 2003.

One day later, the Central Intelligence Agency and Defense Intelligence Agency publicly issued an assessment saying the opposite — that U.S. officials were confident that the trailers were used to produce biological weapons. The assessment said the mobile facilities represented "the strongest evidence to date that Iraq was hiding a biological warfare program." On May 29, 2003, the president repeated the claims from the public intelligence report.

McClellan dismissed the Post article and a report based on it that aired on ABC News Wednesday morning as irresponsible. He said ABC News should apologize and took issue with the way the Post story was written.

"The lead suggested that what the president was saying was based on something that had been debunked, and that is not true," McClellan said. "In fact, the president was saying something that was based on what the intelligence community — through the CIA and DIA — were saying."

McClellan said information for public reports from the CIA comes from many sources and takes time to vet.

"It's not something that, they will tell you, turns on a dime," McClellan said.

The actions of the special team were described to a Washington Post reporter in interviews with government officials and weapons experts who participated in the mission or had direct knowledge of it. The final report remains classified.

The trailers along with aluminum tubes acquired by Iraq for what was believed to be a nuclear weapons program — were primary pieces of evidence offered by the Bush administration before the war to support its contention that Iraq was making weapons of mass destruction.

Intelligence officials and the White House have repeatedly denied claims that intelligence was exaggerated or manipulated in the months before the U.S.-led invasion of Iraq in March 2003. The Iraq Survey Group concluded in 2004 that there was no evidence that Iraq produced weapons of mass destruction after 1991. It said Saddam Hussein's ability to develop such weapons had diminished — not grown — during a dozen years of sanctions before last year's U.S.-led invasion.