Obama will fly to the south-western state to lead a tribute service for the six people who were killed and the 14 wounded in the assassination attempt on congresswoman Gabrielle Giffords, who is fighting for her life in a hospital.
His trip will take place after the family of the alleged gunman Jared Loughner said they were "so very sorry" about Saturday's assault and as surgeons gave an upbeat forecast of Democrat Giffords's condition.
Obama faces a moment fraught with risk but shrouded in political opportunity when he leads the service in Tucson, Arizona, at a time when he is trying to revive his bond with US voters.
His task is complicated by liberal claims that a climate of hate whipped up by conservative figures like Sarah Palin may have tipped Loughner over the edge and exposed malign divisions of US politics.
Presidents, in their symbolic role as head of state and commander-in-chief, are periodically required to invoke unity in a moment of crisis, weaving shocking events into a parable of American history and national mythology.
They have summoned poetry, like Ronald Reagan after a space shuttle disaster in 1986, or prose pulsing with resolve, like George W Bush in his National Cathedral address after the 11 September attacks in 2001.
Such speeches are "a way to take a tragedy and to be sober and sombre but also to use it as a way to bring the country together and to move it forward," said political science professor Jamie McKown.
Obama will likely avoid assigning blame, while honouring the dead and offering counsel for the living.
"The President began working on his speech last night. He is thinking through what he wants to say," a White House official said Tuesday.
"He will devote most of his remarks to memorialising the victims."
As many as 14,000 people were expected to attend the service at the University of Arizona amid tight security. The president was to appear alongside First Lady Michelle Obama and Republican Senator John McCain.
Surgeons meanwhile gave an upbeat outlook for Giffords on Tuesday, as she remained in intensive care after brain surgery following Saturday's attack.
"She's holding her own," said Michael Lemole, the head neurosurgeon who operated on Giffords, adding that she was still responding to simple commands, a key sign for her recovery prospects.
"I'm very encouraged by the fact that she's done so well," he said.
Peter Rhee, head of trauma surgery at University Medical Centre, said doctors had reduced the sedatives administered to the Democratic lawmaker, adding: "She will not die. She does not have that permission from me."
Giffords took a single bullet to the head in the shooting at a public event outside a grocery store in Tucson, which killed six including a federal judge and a nine-year-old girl.
Rhee added that the resources of the entire US military had been offered to help care for the victims, including Giffords, whose husband Mark Kelly is a US Navy captain and astronaut.
Two top military neurosurgeons flew to Tucson on Monday and praised the level of care offered to shooting victims.
Loughner's family, besieged by media since the shooting, meanwhile made their first comment, saying they were "so very sorry" for the victims of their son's attack.
"There are no words that can possibly express how we feel. We wish that there were, so we could make you feel better. We don't understand why this happened," they said in a statement released to media.
"It may not make any difference, but we wish we could change the heinous events of Saturday. We care deeply about the victims and their families, and we are so very sorry for their loss."
Earlier Bill Hileman, whose wife Suzi took nine-year-old Christina Green to the Gifford event outside a Safeway store, said she was suffering harrowing flashbacks about the moment the gunman opened fire.
The schoolgirl was the youngest victim of the shootings, allegedly carried out by 22-year-old Loughner, who appeared in court in the state capital Phoenix on Monday on five charges including murder and attempted murder.