The US president promised that the government would be behind the tornado survivors "every step of the way."
The extraordinarily powerful twister that struck Moore was known as an EF5, ranking it at the top of the enhanced Fujita scale used to measure tornado strength.
"I'm just a messenger here," Obama said during the visit on Sunday, saying "folks are behind you" across America.
He offered moral and monetary support in the wake of last Monday's monstrous tornado that killed 24 people, including 10 children.
Standing with Oklahoma governor Mary Fallin and other state and federal officials, Obama noted the substantial rebuilding job ahead and said "our hearts go out to you".
The White House said the Federal Emergency Management Agency (Fema) already provided $57-million in rebates and incentives to help build about 12 000 storm shelters in Oklahoma.
"These storm shelters can be the difference between life and death," presidential spokesperson Josh Earnest told reporters accompanying Obama to Oklahoma on Air Force One.
For Obama, Sunday's visit had an all-too-familiar ring.
Only five months into his second term, he travelled to the north-east to console people in the wake of the Boston Marathon bombing, and visited Connecticut and Arizona to comfort people traumatised by shooting rampages.
He also undertook his consoler-in-chief role at the site of plant explosions and mine disasters, not to mention a series of natural disasters including Joplin, Missouri, which was hit by a tornado, and the Jersey Shore, which was heavily damaged by Superstorm Sandy last year.
Once on the ground in Oklahoma, Obama urged the American people to make contributions, saying the damage was "pretty hard to comprehend".
Obama noted the tornado destroyed about 1 200 homes and damaged thousands more.
Shortly after his arrival on a partly cloudy day, Obama rode past grassy fields strewn with scattered debris, witnessing devastation so awesome that it appeared as if garbage had literally rained from the sky.
His first stop was the demolished site of the Plaza Towers Elementary School, where seven students were killed when the tornado turned the one-storey building into a heap of bricks, broken concrete and twisted metal.
"I know this is tough," he told superintendent Susie Pierce as he gripped her hand.
As he walked, the demolished school was on his left and on his right, homes as far as the eye could see were reduced to piles of rubble.
Vehicles were turned upside down and toys like a pink doll carriage and children's books were strewn with furniture and ripped out wall insulation.
Every tree had been stripped of its leaves and bark. Obama at one point joined the Lewis family, which lost their home behind the school. He said the important thing was that they survived and could replace their things.
"What a mess," he told their son Zack, a third-grader at the shattered school.
Zack's father, Scott, ran into the school just before the storm hit and ran with his terrified son back to their home's storm shelter.
"You've got some story to tell," Obama told the boy. "This is something you'll remember all your life."
Obama later met privately with victims' families at Moore Fire Department Station No.1, which has turned into a command centre with dozens of first responders sitting at folding tables where fire trucks are normally parked.
Obama marvelled that they saved so many lives "given the devastation".
As he descended the stairs upon landing at Tinker Air Base near here, Obama was greeted first by Fallin, who had said earlier she appreciated the visit, but that her state also needed quick action from Fema.
The Republican governor said that so far, the agency has done a great job of speeding relief and cash assistance to affected families, but said she's concerned about the long run.
Earnest touted the federal contributions so far, including Obama's signing of a disaster declaration within hours of the storm to speed aid from the Fema
Earnest said that 450 Fema personnel were working on the ground in Oklahoma and have delivered 43 000 meals, 150 000 litres of water and thousands of cots, blankets and tarps.
He said 4 200 people applied for disaster assistance and $3.4-million in payments were approved.
Among the tornado victims were 10 children, including two sisters pulled by the strong winds out of their mother's grasp, an infant who died along with his mother trying to ride out the storm in a convenience store and seven students at Plaza Towers.
Many students were pulled from the rubble after the school was destroyed. After Obama departed, Fallin hosted an interdenominational religious service that drew 2 000 people.
"God will give us the ability to mend our broken hearts," Fallin said at the end of the 80-minute service. "We may be knocked down, but we will rise up again, and for that we thank God." – Sapa-AP