In her opening remarks, Rice acknowledged widespread concerns about the war both among members of congress and ordinary Americans.
"I want you to know that I understand and indeed feel the heartbreak that Americans feel at the continued sacrifice of American lives, men and women who can never be replaced for their families, and for the concern of our men and women who are still in harm's way," she said.
"This is a time for a national imperative not to fail in Iraq."
In her testimony, Rice stressed Iraqi obligations for troops, money and the political will to allow the Bush plan to succeed.
She promised oversight, without giving specifics.
"Iraqis are in the lead; we are supporting them," Rice said.
Rice defended the reliance of the Bush administration on the much derided Iraqi government, which has failed to satisfy past US demands for robust action.
She also bluntly said that the team of the Iraqi prime minister had to do a better job on security than in its seven months in power so far.
"They haven't performed in the past... They have to get organised right away, and they are."