On Wednesday, Gates made his first visit to Iraq since being sworn in to his position earlier in the week.
Enemies of liberty
Later on Wednesday, at his traditional end-of-year news conference, Bush conceded that Iraq fighters had thwarted US efforts at "establishing security and stability throughout the country".
He said: "The enemies of liberty ... carried out a deliberate strategy to foment sectarian violence between Sunnis and Shia. And over the course of the year they had success. Their success hurt our efforts to help the Iraqis rebuild their country.
"They set back reconciliation and kept Iraq's unity government and our coalition from establishing security and stability throughout the country."
Bush said he has not decided whether to order a short-term surge in US troops in Iraq in hopes of gaining control of the situation there.
The president said the US would "ask more of our Iraqi partners" in 2007, and he pledged to work with the new Democratic Congress.
In the Washington Post interview Bush declined to put a number on the proposed increase the US military, and disputed the assertion made at the weekend by Colin Powell, his former secretary of state, that "the active army is about broken".
Bush said: "I haven't heard the work 'broken,' but I've the word 'stressed'." He told the newspaper that more ground forces were required to fight the so-called war on terrorism sparked by the attacks of September 11, 2001.
He said: "It is an accurate reflection that this ideological war we're in is going to last for a while, and that we're going to need a military that's capable of being able to sustain our efforts and to help us achieve peace.
"We need to reset our military. There's no question the military has been used a lot.
"And the fundamental question is, will Republicans and Democrats be able to work with the administration to assure our military and the American people that we will position our military so that it is ready and able to stay engaged in a long war, and this ideological struggle?"