Mr Bush last used that format on the first night of military operations that began the March 2003 US-led invasion to topple Saddam Hussein.
The US President rejected calls for a US withdrawal "before our work is done" but acknowledged deep worries about the conflict.
Mr Bush again gave no firm date for US withdrawal from Iraq, although military and political sources are increasingly saying it will probably begin some time next year.
"We would hand Iraq over to enemies who have pledged to attack us, and the global terrorist movement would be emboldened and more dangerous than ever before," he said in excerpts of the speech that he will give at about 1400 AEST (0200 GMT).
Ally growing strong
Mr Bush will tell Americans that Thursday's historic parliamentary elections in Iraq meant the US had "an ally of growing strength in the fight against terror" while cautioning that the historic vote "will not mean the end of violence."
"But it is the beginning of something new: constitutional democracy at the heart of the Middle East," he said.
"I know many Americans have questions about the cost and direction of this war," he said. "Some look at the challenges in Iraq, and conclude that the war is lost, and not worth another dime or another day. I dont believe that."
"Our military commanders do not believe that. Our troops in the field, who bear the burden and make the sacrifice, do not believe that America has lost. And not even the terrorists believe it. We know from their own communications that they feel a tightening noose and fear the rise of a democratic Iraq," he said.
Recent polls have found that a majority of the US public thinks the war, which so far has cost billions of dollars and the lives of at least 2,156 US soldiers, was a mistake, a view reflected in Bush's slumped approval ratings.
A growing chorus of lawmakers has called for everything from an immediate withdrawal to a set of precise benchmarks for a pull-out -- options Mr Bush has rejected and criticised as appeasing terrorists.
Approval ratings sink
Mr Bush's remarks were to cap a month-long public relations offensive in which he delivered four speeches touting progress on the political and economic fronts as well as in training Iraqis to battle a bloody insurgency.
The president's job approval ratings sank to their worst levels ever earlier this year, in part due to Iraq, but rose after Bush acknowledged "mistakes" in US planning and laid out his strategy in unprecedented detail.
On Friday, Mr Bush told PBS television that the US did not need "zero violence" in Iraq before declaring victory but stressed that giving the country's Sunni Arab minority a key role in government would reduce clashes.
"I think if we have a policy of zero violence, it won't be met, but the policy of getting the Iraqis in the fight and marginalizing those who are trying to stir up trouble will be effective," Mr Bush told PBS.
The US is expected to trim troop levels from about 150,000 to 138,000 by end-January, with General George Casey, the US commander in Iraq, to make recommendations on whether further cuts can be made.
That would please some in Mr Bush's Republican Party who worry that the unpopular conflict could cost them dearly in November 2006 legislative and gubernatorial elections.
At least 17 Iraqis were killed over the weekend as violence flared after Sunni and Shiite politicians appealed for unity and warned against sectarian divisions.
US officials hope last week's elections will pave the way for an eventual US exit by encouraging compromises among Sunni, Shiite and Kurdish leaders in the drafting of a final version of a constitution.