(Adds memorial service)
By Jeff Mason
MOORE, Okla., May 26 (Reuters) - Standing by a pile of debris that once was an elementary school, President Barack Obama on Sunday called the destruction last week's tornado wrought in Moore, Oklahoma, "hard to comprehend" and vowed to provide long-term federal help in rebuilding.
The tornado, rated at the top of a five-step scale used to measure the destructive power of twisters, killed 24 people - including seven children at the school site Obama visited. It ripped a 17-mile-long (27-km-long) corridor of destruction through the suburb of Oklahoma City, flattening entire blocks of homes, two schools and a hospital.
"Obviously the damage here is pretty hard to comprehend," Obama said, standing on a block where piles of boards, bricks and cinder blocks that used to be buildings and houses lined the side of the street. Rare items that survived the disaster - a television set, a pink baby carriage - stood in contrast to the wreckage.
The visit to the disaster-shaken town was one in a series of responses Obama has made in recent months to tragedies, including the Boston Marathon bombings last month; a December mass school shooting in Newtown, Connecticut; and the destruction that Superstorm Sandy caused along the Jersey Shore in October.
"Whenever I come to an area that has been devastated by some natural disaster like this, I want to make sure that everyone understands that I am speaking on behalf of the entire country," said Obama, flanked by officials including Oklahoma Governor Mary Fallin. "Everywhere, fellow Americans are praying with you, they're thinking about you and they want to help. And I'm just a messenger here letting you know that you are not alone."
Cars with their bodies dented and windows smashed lay under debris or twisted on their sides. Rising above the wasteland were at least three American flags that had been attached to the rubble, waving in the wind.
Caleb Sloan, 24, who lost his home in the storm, said Obama's words gave him hope that help would be forthcoming.
"He has no choice but to live by his word," Sloan said. "I hope and pray and think he will keep his promises."
SPATE OF STORMS
The May 20 tornado in Moore was the most powerful of a spate of 76 twisters that touched down in 10 states from May 18 through May 20, causing an estimated $2 billion to $5 billion in insured losses, according to disaster-modeling company Eqecat.
The Moore tornado, the deadliest such windstorm to hit the United States in two years, also injured 377 people.
While assuring that residents of the 1,200 homes the storm destroyed would receive extended federal help, Obama also urged lawmakers to maintain funding for the training and equipment that emergency responders rely on in the aftermath of disasters.
"We can't shortchange that kind of ongoing disaster response, we can't just wait until the disaster happens," Obama said. "That's how, in part, we're able to save a lot of lives."
After the president left, the town held its own memorial service at First Baptist Church of Moore that included a performance by the Oklahoma Strong Children's Choir, made up of Moore school children who were affected by Monday's storm. (Additional reporting by Heide Brandes; Writing by Scott Malone; Editing by Daniel Trotta and Philip Barbara)