Mr. Bush said, "The defeat of violence and terror in Iraq is vital to the defeat of violence and terror elsewhere and vital, therefore, to the safety of the American people."
"Now is the time, and Iraq is the place, in which the enemies of the civilized world are testing the will of the civilized world. We must not waver."
The president's comments came during a rare primetime news conference Tuesday night. During the 61-minute exchange with reporters, Mr. Bush faced questions about Iraq, the continuing investigation into pre-Sept. 11 anti-terror efforts and the upcoming election showdown with presumptive Democratic nominee Sen. John Kerry.
He did acknowledge "tough weeks" in the country, blaming the violence on remnants of the deposed Saddam Hussein regime, foreign Islamic militants and supporters of cleric Muqtada al-Sadr. He accused the three of sharing a common goal: "to run us out of Iraq and destroy the democratic hopes of the Iraqi people."
"The violence we have seen is a power-grab by these extreme and ruthless elements. It's not a civil war. It's not a popular uprising. Most of Iraq is relatively stable. Most Iraqis by far reject violence and oppose dictatorship," Mr. Bush said.
But citing the increased violence, the president said he would be willing to deploy more troops to Iraq if commanders requested it.
"If that's what he wants, that's what he gets," Bush said, referring to Gen. John Abizaid, commander of U.S. forces in the region.
He also pledged to continue the mission that had cost some 460 soldiers their lives.
"We will finish the work of the fallen," the president said.
In addition to pledging his continued support for the ongoing operation, he reiterated the U.S. intention to turn over authority in Iraq to a local governing coalition elected in June.
"We have set a deadline of June 30. It is important that we meet that deadline. As a proud and independent people, Iraqis do not support an indefinite occupation and neither does America," Mr. Bush said, warning any change in this deadline would fuel suspicion of American objectives in Iraq.
The president's comments came the same day his Democratic opponent in this year's election criticized the government's Iraq policy in a Washington Post op-ed piece, writing the way the war has unfolded has cost the United States "lives, time, momentum and credibility."
Kerry called for greater internationalization of the situation on the ground in Iraq.
"The United Nations, not the United States, should be the primary civilian partner in working with Iraqi leaders to hold elections, restore government services, rebuild the economy, and re-create a sense of hope and optimism among the Iraqi people," Kerry wrote. "The primary responsibility for security must remain with the U.S. military, preferably helped by NATO until we have an Iraqi security force fully prepared to take responsibility."
During the wide-ranging exchange with reporters, Mr. Bush also defended the work of his administration ahead of the Sept. 11, 2001 terrorist attacks to confront the threat posed by the al-Qaida terror network.
"I look back and I realize we were not on a war-footing and our enemies were at war with us," Mr. Bush said. "This country must go on the offense and stay on the offense."
The Bush administration had faced intense questioning after former counterterrorism chief Richard Clarke accused it of being more interested in war in Iraq than the threat posed by al-Qaida before the attacks.
The Clarke accusations led to the historic testimony of national security adviser Condoleezza Rice before the panel last week and the declassification of a presidential briefing that indicated that al-Qaida hoped to launch attacks within the domestic United States.
But earlier Tuesday, Attorney General John Ashcroft fired back at those who questioned the government's efforts in the days before 9/11. In testimony before the commission, Ashcroft criticized the policies of the Clinton administration, saying the decision to split law enforcement and intelligence efforts had "blinded" the nation to terrorist threats.
"The simple fact of Sept. 11 is this: We did not know an attack was coming because for nearly a decade our government had blinded itself to its enemies," Ashcroft said. "Our agents were isolated by government-imposed walls, handcuffed by government-imposed restrictions and starved for basic information technology."
While not directing comments at President Clinton's efforts, Mr. Bush defended his administration's work to combat terrorism both before and after the attacks that killed nearly 3,000 in New York, Washington and Pennsylvania.
"Had I had any inkling whatsoever that people were going to fly airplanes into buildings, we would have moved heaven and earth to protect the country. Just like we're working to prevent further attacks," Mr. Bush said.
The president, facing reelection in November, also faced a series of questions regarding the upcoming election.
He said he looked forward to the campaign, but said the night's new conference was focused on "explaining the war."
The press conference was only the 11th of his presidency and the first primetime question-and-answer session since the start of the war in Iraq in March of last year.