Updated at 3:30 p.m. ET
Hours before addressing the nation, President Barack Obama told U.S. troops just back from Iraq that his speech outlining the withdrawal of combat forces "is not going to be a victory lap" nor a cause for celebration.
"There's still a lot of work that we've got to do to make sure that Iraq is an effective partner with us," Obama said on Tuesday of his decision to end the nation's combat mission in a war he once strongly opposed.
"The main message I have tonight, and the main message I have to you, is congratulations on a job well done," Obama said.
He also noted that there remained "a tough fight ahead in Afghanistan ... A tough slog."
Before his visit, Obama telephoned former President George W. Bush, who ordered U.S. troops to invade Iraq and topple Saddam Hussein in March 2003. Aides described the phone call from Air Force One as brief and declined to reveal what was said.
"He did think it was important to reach out to President Bush, as he has done on occasion," Denis McDonough, chief of staff for Obama's National Security Council, told The Associated Press.
Ending the combat mission fulfills Obama's campaign promise to bring the war to a close. However a force of roughly 50,000 U.S. troops remains in a training and backup role. All forces are scheduled to be withdrawn by the end of 2011.
Also, Iraq is still torn with violence, and rival political factions have yet to form a government more than six months after national elections.
Obama spoke at a dining hall on this Army base in El Paso, Texas, which has been central to the war effort. The soldiers were among troops who recently returned from Iraq. "Welcome home," Obama said to shouts of "hooah."
He thanked them for their sacrifice.
Noting that the long and unpopular war was a source of "political disagreements" at home, Obama said "the one thing that we don't argue about is the fact that we have the finest fighting force in the world."
"The fact of the matter is that because of the extraordinary service that all of you have done and so many people here at Fort Bliss have done, Iraq has an opportunity to create better future for itself and America is more secure," Obama said.
"The country appreciates you," he said.
Of his 8 p.m. EDT speech, Obama said, "It's not going to be a victory lap. It's not going to be self-congratulatory."
It was part of a calculated White House effort not to encourage parallels to Bush's premature "Mission Accomplished" speech aboard an aircraft carrier in 2003, just three months after the war began.
"A million men and women in uniform have now served in Iraq," Obama noted.
After speaking, the president shook hands with each of the soldiers and family members gathered in the base dining hall, asking where they or their loved ones had served. He also met separately with families of deceased troops.
As he left the room, Obama said, "Thank you for giving me the opportunity to share this time with you and see all of you face to face. Just know that we're all thinking about you and all praying for your families."
To those who will face future missions in Iraq and Afghanistan, Obama said, "We will be relentless in making sure you have what you need to come home safely."
Fort Bliss has seen repeated troop deployments to Iraq. Some of its servicemen and women are among the troops who remain in Iraq.
The administration has called the change of mission in Iraq an important milestone, but not a cause for celebration. "We are in transition," Obama observed.
Obama's comments were echoed by Defense Secretary Robert Gates, who told an American Legion audience in Milwaukee, "This is not a time for premature victory parades or self-congratulation, even as we reflect with pride on what our troops and their Iraqi partners have accomplished."
"I am not saying all is, or necessarily will be, well in Iraq," he continued, noting the continued violence and lack of a new government. The combat mission in Iraq has left more than 4,400 U.S. troops dead and thousands more wounded.
Obama was an early critic of the war, speaking out against it during the U.S. invasion and promising during his presidential campaign to bring the conflict to an end. The White House sees Tuesday's benchmark as a promise kept and has gone to great lengths to promote it as such, dispatching Vice President Joe Biden to Iraq to preside over a formal change-of-command ceremony and raising Tuesday night's remarks to the level of an Oval Office address, something Obama has only done once before.
Appearing on nationally broadcast interviews Tuesday morning, White House press secretary Robert Gibbs repeatedly brushed aside questions about whether Obama would credit Bush's troop surge with helping to pave the way for the withdrawal.
However, McDonough, the Obama national security adviser, told the AP Obama will "recognize the surge as one among many issues that contributed to our ability to protect our interests" in Iraq.
Top Republicans were dubious. "Some leaders who opposed, criticized, and fought tooth-and-nail to stop the surge strategy now proudly claim credit for the results," House GOP leader John Boehner said, in excerpts of a speech he was to give to the American Legion convention in Milwaukee. "Today we mark not the defeat those voices anticipated --but progress."
Since the start of the war, 200,000 personnel from Fort Bliss have deployed to Iraq, serving in every major phase of the war. Fifty-one soldiers from the base died there and many more were wounded.