Washington ? Searching for unity long vanished since the day terrorists astonished America, President Barack Obama will hail national resilience and remember hurting families when he gives the main speech of his Sept. 11 commemorations.

Obama will honor victims at each of the sites where nearly 3,000 people were killed in the 2001 attacks — first at ground zero in lower Manhattan, then in Shanksville, Pa., and at the Pentagon. Yet his only address to the nation will come at night, lasting about 15 minutes during an event at the Kennedy Center in Washington.

The message to expect from the president: America’s character is stronger than the blow inflicted by al-Qaida or any other threat to the country, Obama deputy national security adviser Ben Rhodes said Friday.

The president also will put an emphasis on how lives have changed for the families affected by 9/11 and for the troops who have served since that day. It has been a period in which more than 6,000 service members have died and 45,000 have been wounded in the Afghanistan and Iraq wars.

“This is something that had an extraordinary toll on individual Americans, and that’s what can’t be lost amid the broader debates this country has had,” said Rhodes, who handles strategic communications for the National Security Council and has been involved in shaping Obama’s Sunday remarks.

“You’ve had families who have had to rebuild their lives. You’ve had troops that have had to serve. That’s very much where his focus is going to be.”

Nearly 3,000 people were killed when al-Qaida terrorists hijacked four airplanes and steered them toward the symbols of American democracy and power.

Two planes first crashed into the towers of the World Trade Center, which soon collapsed in fire. One smashed into the Pentagon. And the last one, believed to be intended by hijackers for the White House or the Capitol, plummeted into a Pennsylvania field as passengers fought back to avoid calamity.

The White House insists Obama has no intention to change his plans amid a credible but unconfirmed threat of an al-Qaida attack in New York or Washington around the Sept. 11 anniversary.

After an early departure from Washington, Obama will take part in a formal ceremony Monday morning in New York, joined by former President George W. Bush among other familiar leaders.

Obama is expected to make a short reading, perhaps a few minutes long.

He will then visit Shanksville and the Pentagon, where broader commemorations will have already taken place, to lay wreaths and meet with family members.

In the evening, Obama will give his remarks during the “Concert for Hope,” a celebration of music and readings intended to offer a sense of renewal.

Rhodes said the president, in looking back at the last decade, will seek to reverse the divisiveness of the national debate without dwelling on it.