Bush's plea came in his annual State of the Union address before a joint session of the U.S. Congress, at a time when polls show his approval ratings near an all-time low of just over 30 percent.
Meanwhile, the Senate is preparing to debate two resolutions opposing Bush's decision to send 21,500 additional troops to Iraq, with both measures expected to attract some members of Bush's Republican Party.
'Nothing Is More Important'
Bush said Iraq is at a critical point in its history, with its capital beset by horrific sectarian violence, and that it's time for U.S forces to take stronger action.
The president acknowledged the resistance to his plan to increase the American military presence in Iraq, but said it's the only course that makes sense.
"My fellow citizens, our military commanders and I have carefully weighed the options," Bush said. "We discussed every possible approach. In the end, I chose this course of action because it provides the best chance for success. Many in this chamber understand that America must not fail in Iraq -- because you understand that the consequences of failure would be grievous and far reaching."
Rather than increase forces, some critics have urged Bush instead to begin withdrawing them in an effort to force the Iraqi government to take more responsibility for the country's security.
Bush said that to withdraw prematurely from Iraq would be to leave it in a state of chaos, open to the United States' sworn enemies in the Muslim world, both the Sunnis of Al-Qaeda and the Shi'a of Iran and Hizballah.
"Out of chaos in Iraq would emerge an emboldened enemy with new safe havens, new recruits, new resources, and an even greater determination to harm America," Bush warned. "To allow this to happen would be to ignore the lessons of [the attacks in the United States of] September 11  and invite tragedy. Ladies and gentlemen, nothing is more important at this moment in our history than for America to succeed in the Middle East, to succeed in Iraq, and to spare the American people from this danger."
Baghdad 'Must Follow Through'
As he did on January 10 when he announced his plan for increased troop levels, Bush suggested that the government of Iraqi Prime Minister Nuri al-Maliki has not yet taken sufficient responsibility for that country's security. He noted that Iraq's Shi'a-majority government had made it difficult for U.S. and Iraqi forces to crack down on some Shi'a militias in the Baghdad area.
But the president said that all the people of Iraq -- Shi'a and Sunni alike -- want security, and that it is time for the Iraqi government to provide it.
"Iraq's leaders know that our commitment is not open-ended," Bush said. "They have promised to deploy more of their own troops to secure Baghdad, and they must do so. They pledge that they will confront violent radicals of any faction or political party, and they need to follow through and lift needless restrictions on Iraqi and coalition forces so these troops can achieve their mission of bringing security to all of the people of Baghdad."
Shaky Support In Congress
For the first time in his six years as president, Bush faced an opposition Congress for a State of the Union speech. Democrats won control of both the Senate and House in elections on November 7.
The Senate plans to begin debate today on at least one of two nonbinding resolutions opposing the troop buildup. Both have the support of some members of the Republican Party, including Senator John Warner (Virginia), the influential vice chairman of the Senate Armed Services Committee.
In the face of such opposition, Bush in his speech sought common ground on several domestic issues. They included a program to cut oil consumption by 20 percent in 10 years through the promotion of alternative fuels; a proposal to help more Americans get health insurance; and an immigration plan aimed at making the U.S.-Mexico border more secure while permitting employers to hire some immigrants for jobs not taken by U.S. citizens.
The Democrats chose a new member of the Senate, James Webb (Democrat, Virginia), to give that party's response to the president's address. Webb welcomed Bush's call for bipartisanship, but said Bush himself must be bipartisan as well.
Webb is a veteran of the Vietnam War who served as President Ronald Reagan's secretary of the Navy. In his response, he said he supports a strong hand in the war against international terrorists and opposes a premature withdrawal from Iraq. But he also vehemently opposes the Iraq war.
"The president took us into this war recklessly," Webb said. He disregarded warnings from the national security adviser during the first Gulf War; the chief of staff of the Army; two former commanders of Central Command whose jurisdiction includes Iraq; the director of operations on the Joint Chiefs of Staff; and many, many others with great integrity and long experience in national-security affairs. We are now, as a nation, held hostage to the predictable -- and predicted -- disarray that has followed."
Webb said Bush was being stubborn in his new Iraq policy. What's needed isn't more troops, Webb argued, but more diplomacy with other countries in the Middle East, including Syria and Iran, countries with which Bush has refused to negotiate.
If Bush wants to change his Iraq policy to something less stubborn, Webb said, Democrats will be ready to join him. If not, he said, they'd be glad to show him the way.
The Imam Al-Mahdi Army on parade (epa)
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THE COMPLETE PICTURE: Click on the image to view RFE/RL's complete coverage of events in Iraq and that country's ongoing transition.