Political opponents of the US government have questioned its ability to ensure that full elections are held in Iraq in January 2005.
Violence is still a regular occurrence in many parts of Iraq
Democrats accused Deputy Secretary of State Richard Armitage of "phoney optimism" after he said voting would be open to all Iraqi citizens.
His remarks appeared to contradict Defence Secretary Donald Rumsfeld.
Mr Rumsfeld said on Thursday that the elections might be limited because of the level of violence in Iraq.
Appearing before a Congressional committee, Mr Armitage admitted that any election in Iraq would be "messy".
But he insisted: "We're going to have an election that is free and open - and that has to be open to all citizens."
"And it's got to be our best efforts to get it into troubled areas as well. That's why I think we're going to have these elections in all parts of the country," Mr Armitage said.
He said he had heard nothing of a plan to limit the elections, avoiding the most violent areas.
Mr Armitage was speaking one day after Mr Rumsfeld said it might not be possible to conduct voting in some places targeted by militants.
"So you have an election that's not quite perfect. Is it better than not having an election? You bet," Mr Rumsfeld told senators.
The BBC's Daniela Relph in Washington says relations between the Pentagon and the State Department have themselves been messy of late.
Rumsfeld said Iraq's elections could be "not quite perfect"
Our correspondent says managing a post-war Iraq has seen tensions between sections of the Bush administration, with the State Department usually cautious in public and Mr Rumsfeld often favouring a more direct approach.
Mr Armitage faced hostile questioning from Democrats on the House Appropriations Committee's foreign operations panel.
Congressman Dave Obey from Wisconsin told him it was time to "can the phoney optimism" and added it was going to take "a minor miracle" for the Iraqi elections to take place on time in January.
"This occupation is going to last longer than the Second World War," Mr Obey said.
Congresswoman Nita Lowey from New York said the picture was "bleak".
She accused the Bush administration of misleading Congress and the American people over what could be achieved in Iraq.
She said: "Voter lists haven't actually been created yet. Parties haven't actually been formed."