"A fixed timetable for withdrawal, in my judgment, means defeat," he said.
In a somber, pre-election review of a long and brutal war, Mr. Bush conceded that the United States is taking heavy casualties and said, "I know many Americans are not satisfied with the situation in Iraq."
"I'm not satisfied either," he said at a speech and question and answer session at the White House 13 days before Nov. 7 congressional elections in which Republican control of the House of Representatives and the Senate is at stake.
"Americans have no intention of taking sides in a sectarian struggle or standing in the crossfire between rival factions," Mr. Bush said.
Several Democratic critics have said that is precisely what the administration is risking with an open-ended commitment of American forces, at a time that a year-old Iraqi government gropes for a compromise that can satisfy Sunni, Shiite and Kurdish political interests.
Mr. Bush gave Iraq's Prime Minister Nuri al-Maliki a vote of confidence just hours after Mr. Maliki called his own news conference to reject timetables set on Tuesday for Iraqis to take over from U.S. troops, reports CBS News chief White House correspondent Jim Axelrod. Mr. Bush was cautiously supportive.
In Baghdad, the Iraqi leader took a hard slap at the United States for a raid by U.S. and Iraqi forces on the stronghold of a Shiite militia led by a radical anti-American cleric on whom Al-Maliki relies for political support. Al-Maliki said the raid "will not be repeated."
Al-Maliki also criticized the top U.S. military and diplomatic representatives in Iraq for saying his government needed to set a timetable to curb violence in the country. "I affirm that this government represents the will of the people and no one has the right to impose a timetable on it," he said.
It was just two weeks ago that the president had his last formal, solo White House news conference, and he's never had two of them this close together, reports CBS News White House correspondent Mark Knoller. But with the midterm elections less than two weeks off and control of Congress at stake, he wants his message to be heard.
In his opening moments at the podium in the East Room of the White House, Mr. Bush departed starkly from a practice of not talking about specific deaths in Iraq.
"There has been heavy fighting, many enemy fighters have been killed or captured and we've suffered casualties of our own," he said. "This month we've lost 93 American service members in Iraq, the most since October of 2005. During roughly the same period, more than 300 Iraqi security personnel have given their lives in battle. Iraqi civilians have suffered unspeakable violence at the hands of the terrorists, insurgents, illegal militias, armed groups and criminals."
He called these events "a serious concern to me, and a serious concern to the American people."
For all his fervor about the importance of the military mission in Iraq, Mr. Bush sidestepped when asked whether the Nov. 7 elections should be viewed as a referendum on the war.
"The election is a referendum on which party has a plan to make the economy grow, and which party has a plan to make the American people safe," he said. "If we succeed in Iraq, the country (the United States) is more secure. If we don't succeed in Iraq, the country is less secure."
As he has numerous times while campaigning for Republican candidates, Mr. Bush said of the Democrats, "I do not question their patriotism. I question whether or not they understand how dangerous the world is."
Mr. Bush doggedly defended the job that defense Secretary Donald H. Rumsfeld has done. "I'm satisfied at how he's done all his jobs. He's a smart, tough, capable administrator," the president said.
Then, the commander in chief took full responsibility for the war.
"You asked me about accountability. It rests right here," he said, pointing at his chest for emphasis, "That's what the 2004 campaign was all about."
One Republican strategist close to the White House says this news conference was a big mistake, reports Axelrod. He says he was flooded with calls from Republicans nationwide who say the president needs to do less talking in the campaign's final days, not more.
The news conference was dominated by foreign policy, from Iraq to Iran, Syria and a question about North Korea, the secretive communist regime which recently said it had set off a nuclear test.
"The leader of North Korea likes to threaten," Mr. Bush said. "In my judgment what he's doing is testing the will of the five countries that are working together to convince him there's a better way forward for his people."
The president has refused to authorize one-on-one negotiations with North Korea. Instead, talks occur through a multinational group that includes Russia, China, South Korea and Japan as well as the United States.
Mr. Bush brushed off a North Korean warning for South Korea to stay clear of sanctions against Pyongyang for a nuclear test, declaring "the coalition remains firm."