* Obama continues war on militants begun by Bush
* Two appear together for first time in 18 months
* Obama: U.S. overcomes slavery, fascism, terrorism (Updates with Obama remarks)
By Steve Holland and Jeff Mason
WASHINGTON, Sept 11 (Reuters) - President Barack Obama picked up where his predecessor George W. Bush left off in the war against Islamic militants after the Sept. 11 attacks, and on Sunday both saw the raw emotions that linger 10 years later.
The 10th anniversary of the attacks marked the first time the Democratic and Republican presidents have appeared together publicly since January 2010. But, joined by their wives, the two men made a show of solidarity at Ground Zero in New York, walking in tandem along a memorial pool at the site of the north tower of the World Trade Center. [ID:nS1E78A00A]
They nodded their heads during a moment of silence, the only sound the roaring of the waterfall in the pool.
Afterward, they appeared together behind bullet-proof glass near where the names of those killed on Sept. 11 were read aloud.
Obama read from Psalm 46, and Bush read an 1864 letter written by President Abraham Lincoln to a widow who had lost five sons in the Civil War. The letter said those deaths were "a sacrifice upon the altar of freedom."
Before speaking, Bush put on the podium a badge from New York Port Authority officer George Howard, who died on Sept. 11. Howard's mother gave Bush the badge when he visited Ground Zero three days after the attacks.
The crowd at Ground Zero was somber as survivors of the nearly 3,000 killed at the World Trade Center waved photos of lost loved ones.
Obama maintained the somber mood at an evening service later in Washington, where he praised Bush for emphasizing that the United States was not targeting Islam after the attacks.
"After 9/11, to his great credit President Bush made clear what we reaffirm today: the United States will never wage war against Islam or any other religion," Obama said.
"These past 10 years have shown that America does not give in to fear. The rescue workers who rushed to the scene, the firefighters who charged up the stairs, the passengers who stormed the cockpit -- these patriots defined the very nature of courage."
The president spent most of the day listening rather than speaking.
At Shanksville, Pennsylvania, he faced an upbeat crowd. Obama and his wife Michelle were greeted with cheers and shouts of "USA, USA" in a grassy field where a memorial is being constructed for the passengers and crew of United 93.
"You're my hero," someone yelled from the crowd as the Obamas shook hands and posed for pictures of families of the United 93 victims.
Afterward, the Obamas took a solemn stroll down a trail lined with wildflowers to a large boulder that marked the point of impact for the airliner, which was brought down after a passenger rebellion against the hijackers.
Obama visited all three sites of the attacks. In his final stop at the Pentagon, the president placed a wreath of white flowers on a stand at the "date line" of the memorial outside the vast building. The line says "September 11, 2001 9:37 AM" to mark the time that the plane struck.
Obama then paused and bowed his head in a moment of silence before he and his wife went to greet and take pictures with victims' family members. The small crowd cheered when the Obamas first arrived, but he kept a serious expression duringthe wreath-laying ceremony. A military band played in the background.
In one of the major successes of his presidency, Obama ordered the secret mission in May that led to the death of al Qaeda leader Osama bin Laden.
But neither the death of the man behind the Sept. 11 hijackings nor the decade-old war in Afghanistan to dislodge the Taliban and defeat al Qaeda played a central role in Obama's day. Instead, it was filled with remembering those killed in the attacks -- and looking ahead.
"Decades from now, Americans will visit the memorials to those who were lost on 9/11," Obama said at the evening service at Washington's Kennedy Center.
"They will remember that we've overcome slavery and Civil War; we've overcome bread lines and fascism and recession and riots and Communism and, yes, terrorism. They will be reminded that we are not perfect, but our democracy is durable." (Editing by Christopher Wilson)