NEW ORLEANS — Despite more than $22 million in repairs, a levee that broke with catastrophic effect during Hurricane Katrina is leaking again because of the mushy ground on which New Orleans was built, raising serious questions about the reliability of the city’s flood defenses.

Outside engineering experts who have studied the project told the Associated Press that the type of seepage spotted at the 17th Street Canal in the Lakeview neighborhood afflicts other New Orleans levees, too, and could cause some of them to collapse during a storm.

The Army Corps of Engineers has spent about $4 billion so far of the $14 billion set aside by Congress to repair and upgrade the metropolitan area’s hundreds of miles of levees by 2011. Some outside experts said the leak could mean billions more will be needed and that some of the work already completed may need to be redone. “It is all based on a 30-year-old defunct model of thinking, and it means that when they wake up to this one — really — our cost is going to increase significantly,” an engineer at the University of California at Berkeley, Bob Bea, said.