(CNN) -- Five years after he green-lighted the war in Iraq, President Bush will mark the anniversary by calling the debate over the conflict "understandable" but insisting that a continued U.S. presence there is crucial.
"The answers are clear to me," Bush says, according to excerpts of his speech to be delivered at the Pentagon on Wednesday, the day the war began in 2003.
"Removing Saddam Hussein from power was the right decision, and this is a fight America can and must win."
Almost 4,000 American troops have died in the war, a painful toll that Bush acknowledges in his remarks.
"No one would argue that this war has not come at a high cost in lives and treasure, but those costs are necessary when we consider the cost of a strategic victory for our enemies in Iraq."
Bush contends that the troop surge he ordered in January 2007 has been a success and was necessary at a point when "the fight in Iraq was faltering."
"The surge has done more than turn the situation in Iraq around; it has opened the door to a major strategic victory in the broader war on terror," he says, according to the excerpts.
"For the terrorists, Iraq was supposed to be the place where al Qaeda rallied Arab masses to drive America out. Instead, Iraq has become the place where Arabs joined with Americans to drive al Qaeda out." Watch CNN correspondents recall 'shock and awe' »
Still, large-scale attacks by terrorists and insurgent groups continue in Iraq. Bombings killed six Iraqis and wounded 51 in northeastern Baghdad and Mosul on Tuesday, and the death toll from a Monday suicide bombing in Karbala rose to 50.
In the excerpts, Bush acknowledges critics of the war -- including Democratic presidential candidates Barack Obama and Hillary Clinton -- and says that they "can no longer credibly argue that we are losing in Iraq, so now they argue the war costs too much."
Recently, two economists wrote a column suggesting that the war in Iraq will wind up costing the United States more than $3 trillion.
The opinion piece, published in the Washington Post, was authored by Joseph E. Stiglitz, a Nobel Prize-winning economist who served as chairman of the Council of Economic Advisers under President Clinton, and Linda J. Bilmes, a former chief financial officer at the Commerce Department.
Senate Majority Leader Harry Reid of Nevada cited the $3 trillion figure when criticizing the Bush administration's position on the war.
Bush, in his speech, calls the projected cost "exaggerated."
However, the president says it will take more than weapons to defeat terrorist forces, according to the excerpts.
"So we are helping the people of Iraq establish a democracy in the heart of the Middle East," Bush says.
"A free Iraq will fight terrorists rather than harbor them." E-mail to a friend