He said he was receiving advice, but would reject implementing "ideas that would lead to defeat" - such as "leaving before the job is done".
A high-level review published last week said combat troops could be withdrawn from Iraq by early 2008.
Mr Bush had been due to announce a new strategy next week, but his speech will not now be made until January.
Speaking in Washington after talks with senior Pentagon officials, Mr Bush told reporters he would not give up on the goal of trying to make Iraq a stable democracy.
He admitted that the level of violence in the country, invaded by a US-led coalition in 2003, had been "horrific".
Flanked by Vice-President Dick Cheney and outgoing Defence Secretary Donald Rumsfeld, Mr Bush said US and Iraqi forces had killed or captured about 5,900 insurgents over the past three months.
But he added that "our enemy is far from being defeated".
Turning to the Iraq strategy review, Mr Bush said one reason for the delay was that he wanted to give the incoming Defence Secretary, Robert Gates, an opportunity to provide input.
He said: "I will not be rushed into making a difficult decision, a necessary decision."
He added: "I've heard some ideas that would lead to defeat. And I reject those ideas, ideas such as leaving before the job is done; ideas such as not helping this government take the necessary and hard steps to be able to do its job.
"If we lose our nerve, if we're not steadfast in our determination to help the Iraqi government succeed, we will be handing Iraq over to an enemy that would do us harm."
The review by the Iraq Study Group (ISG) said the current US strategy of "staying the course" was no longer viable.
It offered no hard timetable for a pullout of US forces, despite suggesting the 2008 withdrawal of combat troops.
The bipartisan report's 79 recommendations included holding direct talks with Iran and Syria.
Asked by a reporter about whether the ISG report contained some of bad advice he had mentioned, Mr Bush said his opinion of the review hadn't changed.
He said: "I thought it was interesting that Republicans and Democrats could work in concert to help achieve an objective."
The panel was headed by former Republican Secretary of State James Baker III, and former Congressman Lee Hamilton, a Democrat.