Speaking to reporters on Monday, Rumsfeld said he had the assurances of his top commanders that resistance attacks are under control.
"They feel that the problem is in control, which is not to say that a terrorist can't attack at any time, at any place, using any technique," Rumsfeld said.
He added that the US is in discussions with 14 countries about providing troops to serve in Iraq. The Pentagon last week announced a plan to reduce US forces in Iraq to 105,000 by next May.
Rumsfeld did not identify the 14 countries from which he said the US was seeking troops in addition to the two multinational divisions already in Iraq, but said the decision to send troops would take ‘courage’.
"I recognise that it takes political courage ... It also takes physical courage to put people in Iraq, where people are getting killed and wounded from time to time," he said.
"But let me be clear. The goal is not to reduce the number of US forces in Iraq. It's not to develop an exit strategy. Our exit strategy in Iraq is success. It's that simple"
Donald Rumsfeld, Secretary of Defence
"But let me be clear. The goal is not to reduce the number of US forces in Iraq. It's not to develop an exit strategy. Our exit strategy in Iraq is success. It's that simple," Rumsfeld said.
Rumsfeld said the United States has trained and fielded 118,000 Iraqis serving in security forces including police, border patrol and guards at oil pipelines and other sites, with the number to reach 220,000 under an accelerated training programme.
He has noted Iraqi security forces soon will outnumber the 130,000 US troops in Iraq, and argued that Iraqis must ultimately be responsible for security in their own country.
But US lawmakers including Republican Senator John McCain of Arizona have questioned the wisdom of the Pentagon's strategy of relying heavily on Iraqi security forces with only a few weeks training to combat an insurgency that so far has confounded the American military.
McCain, an influential voice in Congress on defence matters, said rushing Iraqi security forces into the field "sends a signal of desperation." Suggesting it is up to these Iraqis to defeat the insurgency, McCain added, sends a message that an exit strategy is more important than winning.
US forces are fighting resistance forces who have killed 153 American troops since President George Bush declared major combat operations over on 1 May. Resistance attacks also downed two US helicopters in Iraq this month.