NEW ORLEANS — While Willie Ann Williams waited for federal aid to rebuild her home in the hurricane flooded Ninth Ward, it was demolished — apparently by mistake. There was nothing left but bare dirt.

A city official told her family the wood-frame house should not have been torn down, but no one has told them why it happened or what happens next.

Ms. Williams had a building permit and wanted to fix up her house once she received money from the federally funded, state-run Road Home grant program. Now, with no house to repair, she’s living in Franklinton, 70 miles away, and doesn’t know whether she’ll be able to come back, said Ms. Williams’s daughter, Vonder McNeil. Confusion reigns with the approach of an August 29 deadline — the second anniversary of Hurricane Katrina — for the city to tell federal authorities which properties it wants demolished. Homes that were only damaged have wound up on a list of 1,700 condemned properties. Some houses on the list have been gutted for rebuilding or are in move-in condition.

Angry homeowners are besieging City Council members and camping out at city offices. “Do Not Demolish” signs are posted on porches, and some owners are hiring lawyers for a possible legal fight. Homeowner Brick Mason posted his lawyer’s telephone number on his house along with the “Do Not Demolish” sign.

The process of finding and condemning unsafe homes is “not perfect, but it’s working,” city spokeswoman Ceeon Quiett said.

The city says some houses must be torn down to ensure public safety. Some houses still contain moldy debris, the city says. Residents have complained about rats, trash piles, and unkempt, overgrown yards in slow-to-rebound neighborhoods. Some houses look like they might collapse at any time. However, the city cannot define the criteria it uses to declare property an imminent threat to health and safety.

Ms. Quiett said the city’s only intent is to “get consumers to act as quickly as possible so neighborhoods can come back.”

But wide differences in the appearance of condemned properties on the list of 1,700, published in local newspapers, has fueled suspicion.

Karen Gadbois, an advocate with the community group Common Knowledge, said the process goes “beyond the boundaries of reason.” Driving past a row of 10 similar-looking houses along Bayou St. John in the Mid-City neighborhood, she tries to pick out the five that are on the tear-down list, but says there is little to distinguish them from the others.

Since April 2006, about 3,800 properties have been bulldozed by contractors hired by the Army Corps of Engineers under an agreement with the city and Federal Emergency Management Agency. FEMA will pay for work to tear down storm-damaged properties deemed imminent threats, but the city has until August 29 to tell the Corps which properties it wants demolished.

The corps will not contract to tear down houses after September 30, so the cash-strapped city will have to pay for demolition after that, then apply to FEMA for reimbursement. Ms. Quiett said the city feels no pressure to have houses demolished before deadline.

Michael Logue, a spokesman for the Corps, said federal contractors won’t tear down a house if it’s bears a “Do Not Demolish” sign. “We’re not the big bad guys,” he said. “Our job down here is to help the victim.”

Ms. Quiett said she’s not aware of homes being torn down mistakenly. But Logue said there have been cases in which the corps has received a “do not demolish” notice from the city after a property has been razed.

Ms. Quiett said the city is setting aside four days this month for homeowners with properties facing demolition to show proof that they’ve remediated their homes or otherwise addressed health and safety concerns.

“We have compassion in everything we do. Every act of this recovery has been an act of compassion,” she said.