US Secretary of State Condoleezza Rice says Iraq is "worth the investment" in American lives and dollars and said the US could still win the war.
The nation's highest-ranking black government official also said election of a black president was no longer impossible in the US.
Rice was asked whether an additional 100 billion dollars (£50 billion) the Defence Department wants for the Iraq and Afghanistan wars might amount to throwing good money after bad in Iraq.
"I don't think it's a matter of money," Rice said. "Along the way there have been plenty of markers that show that this is a country that is worth the investment, because once it emerges as a country that is a stabilising factor, you will have a very different kind of Middle East."
The top US diplomat made the remarks as Bush faces mounting pressure from the public and members of Congress to find a fresh course in the long-running war. More than three years after the US invasion that deposed Iraqi President Saddam Hussein, the conflict shows no sign of nearing an end and has cost the lives of more than 2,950 American troops and tens of thousands of Iraqis.
Bush conceded this week for the first time that the United States is not winning the conflict, although he said it also is not losing.
"I know from the point of view of not just the monetary cost but the sacrifice of American lives, a lot has been sacrificed for Iraq, a lot has been invested in Iraq," Rice said.
Bush would not ask for continued sacrifice and spending "if he didn't believe, and in fact I believe as well, that we can in fact succeed," Rice said.
Rice said the Bush administration should be remembered for far more than the Iraq war. She ticked off foreign policy commitments and accomplishments that include increased billions to fight Aids and malaria in Africa and a peace deal that ended two decades of North-South warfare in Sudan.
Rice has repeatedly said she will not run for president, despite high popularity ratings and measurable support in opinion polls. Rice would not say whether she would like to see her predecessor, Colin Powell, become a candidate. Powell is a fellow black Republican.
"I'm not going to give Colin any advice, and he's not going to give me any advice on this one," Rice said.
Democratic Senator Barack Obama is the most prominent black politician to emerge as a potential candidate for the 2008 presidential race. Rice was asked whether, watching Obama's rise, she thinks Americans are willing to put a black in the White House.
"Yes, I think a black person can be elected president," Rice said.
She said the first successful black candidate will be "judged by all the things that Americans ultimately end up making their decision on: Do I agree with this person? Do I share this person's basic values? Am I comfortable that this person is going to make decisions when I'm not in the room that are very consequential?"
At the same time, she said, "We should not be naive. Race is still an issue in America. When a person walks into a room, race is evident. It's something that I think is going to be with us for a very, very long time."
Rice said she has no reason to believe North Korea is serious about dismantling its nuclear weapons. "That's what we're testing" in disarmament talks this week that a Japanese envoy described as deadlocked.
"They're signed on to denuclearisation" in an agreement last year that was never implemented, she said. "We'll see whether or not they follow through," Rice said.
A watered-down UN sanctions resolution against Iran would have more than symbolic value, Rice said. But she said she has no assurances that Russia will vote for the resolution this week despite long efforts to satisfy Moscow's misgivings about sanctions.
"The Russians say that they want to prevent the Iranians from perfecting technologies that could lead to a nuclear weapon," Rice said. "I take them at their word, and that's why I think ... they will reflect that in their support for a resolution."
She said she is confident all members of the United Nations members will enforce the sanctions once passed, no matter how they voted on the resolution.