Airborne mold has reached such high levels here since Hurricane Katrina that the federal government should monitor it closely and give protective gear to residents unaware of the health risk, a national environmental group said Wednesday.

Test samples in 14 locations across New Orleans last month found excessive concentrations of mold spores indoors and out, the Natural Resources Defense Council reported. An indoor count in a neighborhood hardly touched by floodwaters registered even higher than a reading in one of the worst-hit areas.

Moisture fosters the spread of mold. About 80% of the city was flooded after Katrina's surging waters broke through levees and floodwalls along canals. Mold is a naturally occurring growth that discharges spores the way plants release pollen. Like pollen, the spores can trigger allergies or episodes of asthma.

In high concentrations, mold can be a serious health risk for people with asthma, allergies, respiratory problems or immune system deficiency, said Gina Solomon, a San Francisco physician and professor of medicine who led the research. Also at risk: chemotherapy patients and the elderly.

Solomon said the outdoor readings, taken Oct. 15-17, were at least two to four times higher than normal for New Orleans, where the warm, humid climate promotes mold growth. Indoor results were worse. The findings "are really disturbing to me," she added.

The highest outdoor reading was 102,000 mold spores per cubic meter in the Mid-City neighborhood, where city officials this week lifted restrictions on overnight stays by returning evacuees. The National Allergy Bureau classifies a mold spore count above 50,000 as "very high," its highest level.

Solomon said mold is "the leading culprit" for a condition known locally as "Katrina cough." Some people have reported a nagging cough, sore throat, runny nose and other symptoms.

Federal, state and local agencies have posted advice on the Internet for returning residents to wear masks and protective clothing in moldy homes. Fliers detailing precautions have been distributed and radio announcements aired.

But the council said the federal government should do more. Solomon said it should set up mold monitoring and give returning residents protective clothing, mold-rated respirators and other gear.

Jill Smith, spokeswoman for the Centers for Disease Control and Prevention, lead federal agency on mold in the hurricane zones, said issuing such gear is a state and local matter. She said the agency is focusing on the types of molds being found here rather than the quantity, because certain varieties are a greater health risk. She said the CDC has done some indoor monitoring of mold but the results are not ready for release.

Pam Dashiell, a resident of New Orleans' hard-hit Lower 9th Ward, said many people coming home to clean up aren't taking precautions because they haven't heard the warnings. "I see people all the time without masks or suits, even with bare hands sometimes," she said.