Mr Mandelson apparently believed he had been set up as a "fall guy" to take the blame if the project collapsed, and he felt he was losing the backing of the Prime Minister as the public failed to support the Dome.
His worries are revealed in a television documentary that also exposes how the head of the Dome's advisory group, Michael Grade, warned the project's Faith Zone could "fall flat on its face" because of compromises over its content.
Yesterday the Cabinet Office minister Lord Falconer of Thoroton denied he had been brought in as a "fixer" to save a faltering project. He credited Mr Mandelson with doing the groundwork to ensure the success of the Dome.
But in next month's BBC2 documentary, Trouble at the Big Top, Mr Mandelson is seen to have serious doubts about the Dome despite his public pronouncements that it would capture the imagination of Britain and the world.
At one point, he ponders why he is doing the job and says: "I was a minister and I was told to. I'd be a good fall guy if it all went wrong."
He worried he was losing the support of Tony Blair and of Jennie Page, chief executive of the Dome's operator, the New Millennium Experience Company. Mr Mandelson felt she wanted to hit him with a rolling pin.
Lord Falconer said yesterday the Dome and its transport links would be ready on time. He dismissed as "complete rubbish" suggestions that he had to save the project from its association with Mr Mandelson's Cool Britannia campaign.Reuse content