America's former ambassador to the United Nations, John Danforth, made the admission in an interview in which he confirmed that the Bush administration's stance was dictated by domestic considerations.
The Bush administration aligned its position last year with that of the US Congress, which urged President Bush in a vote in July to call the mass killings and ethnic cleansing in western Sudan "by their rightful name: genocide".
At that time, more than one million black Africans had been forced from their homes by militias allied to the Islamist government in Khartoum, and 60,000 people had been killed. The UN had described Darfur as "the worst humanitarian disaster in the world" but declined to call it genocide.
Mr Danforth was asked by the BBC's Panorama programme whether the characterisation of genocide by President Bush and the Secretary of State, Colin Powell, had hindered a resolution to the Darfur conflict because of the loaded nature of the word.
"I didn't think it had much of an effect one way or another. I just thought that this was something that was said for internal consumption within the US. I did not think it would have very much effect within Sudan," Mr Danforth said. Asked whether "internal consumption" referred to the kind of language that would have appealed to the Christian right, he replied: "Right."
In the same programme, the Development Secretary, Hilary Benn, admits that in Darfur, "we haven't got it right in this instance." The conflict is still simmering, more than 2 million people have fled their homes and the UN Security Council is divided on what to do.
"Panorama - 'Never Again': Darfur and The Promise Broken" will be broadcast on BBC1 tomorrow at 10.15pmReuse content