The US defence secretary has suggested Iraq may only be able to hold limited elections in January, omitting areas where violence is most severe.
US troops have been increasingly under fire from Iraqi insurgents
Donald Rumsfeld told senators it might not be possible to conduct voting in some places targeted by militants.
Earlier, interim Iraqi Prime Minister Iyad Allawi and US President George W Bush ruled out delaying the vote.
Mr Allawi told a joint session of Congress that Iraq was succeeding in establishing freedom and democracy.
But Democratic presidential candidate John Kerry accused Mr Bush and Mr Allawi of trying to fool American voters by saying things were getting better in Iraq.
The BBC's Justin Webb, in Washington, says Mr Rumsfeld has been kept out of the limelight in recent months but now has stepped back in with characteristic brio.
Mr Rumsfeld told the Senate Armed Services Committee: "Let's say you tried to have an election and you could have it in three quarters or four fifths of the country but some places you couldn't because the violence was too great.
"Well, so be it, nothing is perfect in life, so you have an election that's not quite perfect. Is it better than not having an election? You bet."
The other big issue being discussed in Washington is the troop level necessary to support the elections.
Mr Rumsfeld confirmed that the commander of US forces in the region might ask for reinforcements during that time.
Allawi and Bush presented a united front over Iraq
Earlier, President Bush said that Iraq's "decisive moment was approaching.
As the January deadline for elections in Iraq nears, Mr Bush said the US must remain in Iraq to fight insurgents, who he said were part of the global terror threat.
"If we stop fighting the terrorists in Iraq, they would be free to plot and plan attacks elsewhere, in America and other free nations," he said.
The president was speaking after a meeting with Mr Allawi - who told Congress that most of his country was ready to "hold elections tomorrow" if necessary.
He added that the violence was concentrated in just three of Iraq's 18 provinces.
He said that despite a "tough struggle with setbacks" the overwhelming majority of Iraqis were grateful for what Americans had done for their country.
"Today, we are better off, you are better off, the world is better off without Saddam Hussein. Your decision to go into Iraq was not an easy one, but it was the right one."
Mr Allawi later said he would seek an explanation from United Nations Secretary-General Kofi Annan about his attitude to Iraq's elections when the two meet on Friday at the UN.
In a recent BBC interview, Mr Annan appeared to express doubts about the Iraqi poll due in January.
"You cannot have credible elections if the security conditions continue as they are now," he said.
Reacting to the statements by Mr Allawi and Mr Bush, Democratic presidential candidate John Kerry rejected their assessment of the situation in Iraq.
He said things were "not getting better and we need to change the course to protect our troops and to win".