Without providing any specific details of the 50-page report, one official who read it said it contained "a significant amount of pessimism", the New York Times reported on Thursday.
The National Intelligence Estimate, prepared by the National Intelligence Council, outlines three possibilities for Iraq through the end of 2005.
The worst scenario foresees developments that could lead to civil war, while the most favourable predicts a tenuous stability in political, economic and security terms, officials familiar with the report told the US daily.
The assessments, made before the recent surge in violence in Iraq and the US military death toll there topping 1000, appear to conflict with Bush's upbeat description of the US-led effort to stabilise and democratise Iraq.
After a car bombing on Tuesday in Baghdad that killed more than 70 people, Bush told a campaign rally in Colorado: "Despite ongoing acts of violence, Iraq now has a strong prime minister, a National Council, and national elections are scheduled in January."