"Governments on all levels fell short of their responsibilities," the president said in a speech in New Orleans. "A year ago I made a pledge: that we will learn the lessons of Katrina and do what it takes to help you recover."
"We're addressing what went wrong," he told residents at a high school gymnasium.
"Unfortunately, the hurricane also brought terrible scenes we never thought we'd see in America," Mr. Bush said. "Citizens drowned in their attics. Desperate mothers crying out on national TV for food and water. A breakdown of law and order and a government, at all levels, that fell short of its responsibilities.
"When the rain stopped ... our television screens showed faces worn down by poverty and despair. And for most of you, the storms were only the beginning of our difficulties."
He also made a pitch for improving New Orleans' education system during the rebuilding and for his economic programs in general.
"I congratulate the people here, but there's more work to be done," he said.
Earlier, President and Mrs. Bush sang a hymn and lit candles inside St. Louis Cathedral in New Orleans' French Quarter Tuesday, as part of citywide remembrances on the first anniversary of Hurricane Katrina.
reports Mr. Bush listened as Archbishop Alfred Hughes tried to answer those who ask if the storm was the will of God.
"We ask not why has God allowed this disaster, but how does God want us to respond to it," Hughes said.
Outside the cathedral, , and Mayor Ray Nagin told the crowd the anniversary was a difficult day for everyone, including himself.
"Trust me. We will get through it. We will get through it together," he said.
"I felt like I needed to be here. It's like a funeral, and life goes on after today," said Gayla Dunn, 33, of New Orleans.
Hurricane Katrina made landfall 65 miles south of the city in the tiny fishing village of Buras. Within hours, New Orleans' protective levees collapsed, causing one of the worst natural disasters in U.S. history and the deaths of more than 1,800 people.
At each of the city's broken levees, they tossed wreaths of flowers, sending them bobbing into calm, black water.
Under an equally calm sky in Gulfport, Miss., the community remembered 14 residents lost to the storm. Firefighters and police officers carried 14 red roses, placing them in a ceremonial vase.
The daughter of an 83-year-old man who drowned in his home last year clutched one of the roses after the service. "I'm hoping this is a step forward. I've been crying for a year and I'm tired of crying," said Carolyn Bozzetti, 60.
In St. Bernard Parish, where just about every building was flooded after the levees buckled, 400 people gathered for mass at Our Lady of Prompt Succor, a church named for the saint to whom Catholics in Louisiana traditionally pray for protection from hurricanes. The water had risen just high enough to graze the feet of a golden statue of Our Lady Of Prompt Succor beside the altar.
The working class community adjacent to New Orleans' Ninth Ward lost 129 people to the flooding.
"We are alive," said the Rev. Danny Digal. "One year, and we're still here."
Others planned to mark the anniversary privately.
"I'm going to pray to the good Lord that he put his arms around the levees. I'm praying that he hug the levees tight so they don't break again, that he keep us safe," said 58-year-old Doretha Kitchens, whose home in the Lower Ninth Ward was submerged under a 10-foot (3-meter)wave.
Katrina grazed Florida before making landfall on Aug. 29, 2005, in Buras, a fishing village south of New Orleans on one of the fingers of land jutting out into the Gulf of Mexico. Entire blocks of houses, bars and shops vanished, whipped into the Gulf by a wall of water 21 feet high.
But the worst was yet to come: The industrial canal began to leak, and when two sections of the wall fell, a muddy torrent was released that yanked homes off their foundations.
Throughout the city, other parts of the levee system began to fail. With each breach came a gush of water, until 80 percent of the city was submerged.
Nearly 1,600 people died just in Louisiana and another 231 were killed in Mississippi, while the rest of the nation watched in horror as survivors begged to be rescued from rooftops and freeway overpasses. Forty-nine bodies remain unidentified in a Louisiana morgue.
The reminders of the destruction — and how far the city still has to go — are everywhere. White trailers still line driveways in neighborhoods where debris is stacked up in piles and unchecked weeds have overtaken abandoned houses. Only half the population has returned. Many of those who have have elected to take on long-time financial hardship and start rebuilding, rather than waiting any longer for federal assistance, reports .
Emergency medical care is doled out in an abandoned department store, while six of New Orleans' nine hospitals remain closed. It's estimated that only half of New Orleans' 2,300 doctors have returned since the storm — and there are even fewer nurses. "It's full out, emergency medicine, sick people and lots of 'em, all day long," emergency services specialist Dr. Tracy Legros.
Only 54 of 128 public schools are expected to open this fall.
First lady Laura Bush says her husband understands that many people in the area blame him for the slow response.
"He's very committed to the Gulf Coast. And I actually think that the people in the Gulf Coast know that," she said on CBS News' The Early Show.
"The outpouring of support for the people of the Gulf Coast from Americans and from people around the world is unprecedented," Bush told Early Show co-anchor Harry Smith. "I know that the people of the Gulf Coast know that the American people are standing with them."
But Mayor Ray Nagin is promising the good times will roll again in New Orleans.
"We will have probably one of the biggest construction booms that they've ever had, so we will have an updated city with the quality of life issues that people have in other cities," he said on The Early Show. "But this is for pioneers. This is hard work and it's going to take us a good three to five years to rebuild this city or to get it to some semblance of what we were accustomed to prior to Katrina hitting us."