Obama: 'We will have to change'

• The president said the nation must change to prevent future tragedies
• Obama also met with victims' families, first responders
• Obama has spoken after three other mass shootings

President Obama told survivors of the Connecticut elementary school shooting on Sunday that the nation's "love and prayers" are with them and their children -- and told the nation that "we will have to change" to prevent such horror in the future.

"We can't tolerate this any more," Obama told families during an interfaith service at a high school in Newtown, Conn.. "These tragedies must end, and to end them we must change ... We can't accept events like this as routine."

The president, tearful at times, did not offer specific policies, but said in the coming weeks he will use whatever powers he can -- working with others -- "in an effort aimed at preventing more tragedies like this."

Earlier, performing the saddest of presidential duties, Obama met privately with relatives of the 20 children and six adults who lost their lives in Friday's mass shooting at Sandy Hook Elementary School. The shooter and the shooter's mother also died.

In his personal and emotional address at the memorial service, Obama emphasized the deaths of innocent children. A father of two daughters, Obama told the families: "I am very mindful that mere words cannot match the depths of your sorrow, nor can they heal your wounded hearts .. I can only hope that it helps for you to know that you are not alone in your grief."

Obama praised teachers who tried to protect their students during moments of terror, as well as students who showed their own special brand of courage during the attack. He ended his remarks by reciting the first names of the children killed, and said, "God has called them all home.

"For those of us who remain," Obama said, "let us find the strength to carry on and make our country worthy of their memory."

The president, noting that this was the fourth time he has traveled to the site of a mass shooting, said this latest act of violence -- committed mostly against elementary school children -- raises "hard questions" for the nation as a whole.

"Can we honestly say that we're doing enough to keep our children, all of them, safe from harm?" Obama said.

He later answered his own question: "If we're honest without ourselves, the answer is no. We are not doing enough. And we will have to change."

At another point, he asked: "Are we really prepared to say that we're powerless in the face of such carnage, that the politics are too hard?"

FULL COVERAGE:Latest developments on aftermath of Conn. school shooting

In addition to the families, Obama spoke earlier with police officers and other first responders to the tragedy. The White House declined to release details of the president's meetings, which also took place at Newtown High School.

Audible sobs could be heard during the president's address in the school auditorium. Many members of the crowd wore lapel ribbons of green and white, the colors of Sandy Hook Elementary School.

A large number of elementary school-age children also attended, some of them clutching teddy bears and other cuddly toys. At the door, members of the Red Cross handed out stuffed dogs.

Members of the crowd stood and applauded as first responders, family members, and Obama entered the auditorium.

One of the earlier speakers, Connecticut Gov. Dan Malloy, told the crowd that Obama had told him that Friday was "the most difficult day of his presidency." (In his remarks that day, Obama had to pause and wipe away tears.)

On the stage, in front of the presidential podium: A table with 26 candles encased in glass, one for each shooting victim. A pianist played "Amazing Grace."

Outside the high school, people listened to Obama's speech on a loudspeaker while wrapped in blankets and holding candles.

Sen. Joe Lieberman, I-Conn., also attending the memorial service, told reporters he supports creation of a national commission on violence in the wake of this, the latest mass shooting.

"These events are happening more frequently, and I worry that if we don't take a thoughtful look at them, we're going to lose the hurt and the anger that we have now," Lieberman said. "And that includes looking at violence in the entertainment culture, mental health services and, of course, gun laws."

On the hill leading up to the school, several houses featured visible Christmas lights -- but most were dark.

In his remarks, Obama also reference other recent mass killings.

The president also met with family members and spoke after the 2009 serial killings at Fort Hood, Texas, which killed 13 servicemembers; the 2010 shooting in Tucson that killed six people and wounded Rep. Gabrielle Giffords, D-Ariz., and the July shooting at a movie theater in Aurora, Colo., that left 12 people dead.

In his Saturday radio address, Obama said: "As a nation, we have endured far too many of these tragedies in the last few years."