BAGHDAD — On a farewell trip to Iraq, President George W. Bush said Sunday the war has been hard, but was necessary to protect the U.S. and give Iraqis hope for a peaceful future.

Bush visited the Iraqi capital just 37 days before he hands the war off to President-elect Barack Obama, who has pledged to end it. At the end of nearly two hours of meetings at an ornate, marble-floored palace along the shores of the Tigris River, Bush defended the war, now in its sixth year.

"The work hasn't been easy, but it has been necessary for American security, Iraqi hope and world peace," the president said. "I'm just so grateful I had the chance to come back to Iraq before my presidency ends."

But in many ways, the unannounced trip was a victory lap without a victory. Nearly 150,000 U.S. troops remain in Iraq fighting a war that is remarkably unpopular in the United States and across the globe. More than 4,209 members of the U.S. military have died and the war has cost U.S. taxpayers $576 billion since it began five years and nine months ago.

After an arrival ceremony, Bush began a rapid-fire series of meetings with top Iraqi leaders. The president wanted to highlight a drop in violence in a nation still riven by ethnic strife and to celebrate a recent U.S.-Iraq security agreement, which calls for U.S. troops to withdraw by the end of 2011.

Air Force One, the president's distinctive powder blue-and-white jetliner, landed at Baghdad International Airport in the afternoon local time after a secretive Saturday night departure from Washington. In a sign of modest security gains in this war zone, Bush received a formal arrival ceremony — a flourish absent in his three earlier trips.

Referring to Iraqi President Jalal Talabani, seated beside him, and the country's two vice presidents, Bush said: "I've known these men for a long time and I've come to admire them for their courage and their determination to succeed."

Bush's meetings at the palace were held as the sun set outside and darkness fell over Baghdad. Talabani called Bush "our great friend," who "helped to liberate" Iraq. "Thanks to him and his courageous leadership, we are here," Talabani said in heavily accented English.

Bush and Iraqi Prime Minister Nouri al-Maliki planned a ceremonial signing of the security agreement — a "remarkable document," according to Bush's national security adviser, Stephen Hadley. He said the pact was unique in the Arab world because it was publicly debated, discussed and adopted by an elected parliament.

Hadley said the trip proved that the U.S.-Iraq relationship was changing "with Iraqis rightfully exercising greater sovereignty" and the U.S. "in an increasingly subordinate role."

The Bush administration and even White House critics credit last year's military buildup with the security gains in Iraq. Last month, attacks fell to the lowest monthly level since the war began in 2003. Still, it's unclear what will happen when the U.S. troops leave. While violence has slowed in Iraq, attacks continue, especially in the north. At least 55 people were killed Thursday in a suicide bombing in a restaurant near Kirkuk.

For Bush, the war is the issue around which both he and the country defined his two terms in office. He saw the invasion and continuing fight — even after weapons of mass destruction, the initial justification for invading Iraq, were not found — as a necessary action to protect Americans and fight terrorism. Though his decision won support at first, the public now has largely decided that the U.S. needs to get out of Iraq.

It was Bush's last trip to the war zone before Obama takes office Jan. 20. Obama won an election largely viewed as a referendum on Bush, who has endured low approval ratings because of the war and more recently, the U.S. recession.

Obama has promised he will bring all U.S. combat troops back home from Iraq a little over a year into his term, as long as commanders agree a withdrawal would not endanger American personnel or Iraq's security. Obama has said that on his first day as president, he will summon the Joint Chiefs of Staff to the White House and give them a new mission: responsibly ending the war.

Obama has said the drawdown in Iraq would allow him to shift troops and bolster the U.S. presence in Afghanistan. Commanders there want at least 20,000 more forces, but cannot get them unless some leave Iraq.

After a 10 1/2 hour fight, Bush was met at the airport by U.S. Ambassador Ryan Crocker and the top U.S. commander Gen. Raymond Odierno. The president then climbed aboard a helicopter for a five-minute flight to the presidential palace.

The trip was conducted under heavy security and a strict cloak of secrecy. People traveling with the president agreed to tell almost no one about the plans, and the White House released false schedules detailing activities planned for Bush in Washington on Sunday.

Bush's visit came after Defense Secretary Robert Gates' unannounced stop in Iraq on Saturday, at a sprawling military base in the central part of the country. Gates will be the lone Republican holdover from the Bush Cabinet in the Obama administration.

The new U.S.-Iraqi security pact goes into effect next month. It replaces a U.N. mandate that gives the U.S.-led coalition broad powers to conduct military operations and detain people without charge if they were believed to pose a security threat. The bilateral agreement changes some of those terms and calls for all American troops to be withdrawn by the end of 2011, in two stages.

The first stage begins next year, when U.S. troops pull back from Baghdad and other Iraqi cities by the end of June.

Odierno said Saturday that even after that summer deadline, some U.S. troops will remain in Iraqi cities. They will serve in local security stations as training and mentoring teams, and so will not violate the mandate for American combat forces to leave urban areas, he said.

Iraq's Defense Ministry said Sunday that U.S. commanders would have to get Baghdad's permission for keep the troops there.