In a 3,000-word front-page article the newspaper said it "did not pay enough attention to voices raising questions about the war".

The admission followed similar articles by the New York Times and New Republic magazine, which said they were either insufficiently rigorous, gullible or more concerned with getting stories first than getting them right.

Leonard Downie, the Post's executive editor, said: "We were so focused on trying to figure out what the administration was doing that we were not giving the same play to people who said it wouldn't be a good idea to go to war ... Not enough of those stories were put on the front page. That was a mistake on my part. [Across the country] the voices raising questions about the war were the lonely ones. We didn't pay enough attention to the minority."

The Post's editorials favoured the war. The day after Colin Powell, the US secretary of state, made his pivotal presentation to the UN, its leader said: "It is hard to imagine how anyone could doubt that Iraq possesses weapons of mass destruction."

Its more sceptical news articles were relegated to the back of the paper, while the White House's pronouncements, which have since been proved erroneous, were given front-page treatment.

"The result," said media correspondent Howard Kurtz in the Post, "was coverage that, despite flashes of groundbreaking reporting, in hindsight looks strikingly one-sided at times."

Michael Massing, whose forthcoming book Now They Tell Us rebukes the American press for its coverage of the war, said: "On the key issue of Iraq's weapons of mass destruction the paper was generally napping along with everyone else. It gave readers little hint of the doubts that a number of intelligence analysts had about the administration's claims regarding Iraq's arsenal".

Inside the Post the criticism focused on misplaced priorities. Thomas Ricks, the Pentagon correspondent, told Kurtz: "There was an attitude among editors: 'Look, we're going to war, why do we even worry about all this contrary stuff?'"

Others in the paper were less contrite.

"I believe we pushed as hard or harder than anyone to question the administration," said Liz Spayd, the assistant managing editor for national news.

"Do I wish we would have ... pushed harder and deeper into questions of whether they possessed weapons of mass destruction? Absolutely. Do I feel we owe our readers an apology? I don't think so."