Maliki on Wednesday angrily rejected US-imposed "benchmarks" for disarming the militias and assuming responsibility for security within 12 to 18 months.
The US ambassador in Iraq had said he hoped such a plan would be in place by December, and senior US officials in Washington said they were pressing Iraqis on it.
But Rumsfeld testily denounced questions at a news conference about the differences as aimed at stirring controversy before the US mid-term elections November 7.
"It's a political season," he said. "And everyone's trying to make a little mischief out of this, and turn it into a political football."
He said the two sides had been in discussion for a long time on the way forward in Iraq but indicated there were no formal targets or set dates, observing that failure to meet them would expose the effort to criticism.
"So you ought to just back off, take a look at it, relax, understand that it's complicated, it's difficult," he said.
"Honourable people are working on these things together. There isn't any daylight between them. They'll be discussing this and discussing that. They may have a change there, a change here. But it'll get worked out," he said.
Surging sectarian violence in Iraq and rising US casualties have made the deteriorating situation in Iraq a prime issue in an election campaign in which Republican control of Congress is at stake.
Among the questions raised by critics is whether the administration's strategy of standing up Iraqi security forces so US forces can stand down is bearing any fruit.
US commanders have had to repeatedly shelve plans to reduce US forces levels in Iraq, which now stand at more than 140,000 US troops because Iraqi forces failed to quell, and in some cases fomented, the sectarian violence in Baghdad.
Rumsfeld acknowledged that the Iraqi security forces had failed to meet expectations in some instances, and have had to be bailed out by coalition forces.
But, he said, "anyone who runs around denigrating the Iraqi security forces and minimising their capability is making a mistake and doesn't understand the situation."
Rumsfeld said he had recommended budget increases and more capable weapons systems for the Iraqi security forces as a result of a recently completed review into the way they are equipped and organised.
He said he also recommended accelerating the pace at which those changes are made to "try to achieve some of it still sooner, at a higher level than had been previously been estimated."
Public rifts, meanwhile, have opened between the Iraqi government and coalition forces over raids targeting leaders of Shia death squads.
Al-Maliki demanded an investigation Wednesday after Iraqi special forces and US military advisers raided locations in Sadr City, a stronghold of radical Shia cleric Moqtada Sadr, in search of a missing US soldier.
Rumsfeld said Maliki, whose government includes Sadr loyalists, was wrestling with how to deal with the cleric and his militia, which US commanders have identified as the main source of sectarian violence in Baghdad.
Maliki's hope, Rumsfeld said, "understandably, quite logically, is to try to achieve a good portion of that politically, through discussion, through compromise, through a reconciliation process, and then, where necessary, use force."

Copyright AFP (Agence France-Presse), 2006