The ceremonies were tinged with a recognition of how much the city has rebuilt since Katrina's floods, as well as fear that another disaster could be looming.
"We look ahead to a better day, as we also prepare ourselves for another threat," Mayor Ray Nagin said as he helped guide a gleaming coffin into a mausoleum.
Tropical Storm Gustav was swirling near Jamaica on Friday after being blamed for 67 deaths in its path. Forecasters said it could hit the Louisiana coast early next week as a major hurricane and city and state officials were preparing for possible weekend evacuations -- the first in the state since Katrina hit in 2005.
About 200 people attended the ceremony. Many rang hand-held bells at 9:38 a.m., the time that levee breaches that inundated the city are believed to have begun.
"I think God is reminding us that on the eve of Katrina, God can bring nature back," said Russell Honore, the retired Army General who headed up rescue efforts three years ago.
Preparations for Gustav forced cancellation of other Katrina memorials Friday, including a jazz funeral that was to have been part of the memorial service. Instead, a lone trumpeter played "Amazing Grace."
In coastal Mississippi, also devastated by Katrina, a morning memorial was held in the town of Waveland, but in neighboring Bay St. Louis, officials chose not to mark the anniversary.
"We decided not to look backward. We decided to look forward with all the progress we've made," said Harold "Buz" Olsen, director of administration for Bay St. Louis.
As Gustav churned, the National Guard was scheduled to begin convoying into New Orleans, while some nursing homes and hospitals planned to start moving patients further inland and the state began moving 9,000 inmates from coastal lockups.
Mississippi Gov. Haley Barbour called Friday for a mandatory evacuation of Katrina victims still living in temporary homes along the state's 70-mile coast. The evacuations, which will begin this weekend, also apply to some residents in 2,800 cottages built as an alternative to trailers. The mayor of Grand Isle, La., a town typically among the first to evacuate when bad weather threatens, called for a voluntary evacuation.
An evacuation order for New Orleans was likely, Nagin said, but not before Saturday. Meanwhile, residents of areas further south could be told to leave starting Friday, Gov. Bobby Jindal said.
Federal, state and local officials expressed confidence that plans put in place since Katrina would protect residents.
"What you're going to see is the product of three years of planning, training and exercising at all levels of government, starting with the local and the state level and leading up to the federal level," U.S. Homeland Security Secretary Michael Chertoff told ABC's "Good Morning America" on Friday from New Orleans. "So we're clearly better prepared."
New Orleans said it is prepared to move 30,000 residents in an evacuation; estimates put the city's current population between 310,000 to 340,000 people. There were about 454,000 here before Katrina hit. Unlike Katrina, there will be no massive shelter at the Superdome, in fact, no shelter at all was planned for the city. It was unclear what would happen to those left behind.
The first 150 of 700 buses to move residents inland arrived at a staging area near New Orleans on Thursday.
Forecasters reiterated that storm projections days ahead of a storm are extremely tenuous. National Hurricane Center specialist Richard Knabb cautioned that the track forecast is still uncertain and the final landfall is possible throughout the northern Gulf Coast.
At 11 a.m. EDT, the center of Gustav was about 165 miles east-southeast of Grand Cayman. It had top sustained winds near 65 mph.
But forecasters said for the first time that there's a better than ever chance that New Orleans will feel at least tropical storm-force winds. There was much less confidence in whether the city would get hit by hurricane-force winds.
Melissa Clark, who lives in neighboring Jefferson Parish, said she's leaving Friday with her family to stay with friends in Clinton, Miss. -- evacuation order or not. Her husband, who works in maintenance at a nearby hospital, will stay behind.
"I'm not taking any chances this time," the 35-year-old mother of three teenagers said as she waited fifth in line at a Wal-Mart gas station Thursday.