NEW YORK — Nearly a year after rushing to the World Trade Center, nearly 600 firefighters and paramedics remain on leave or limited duty because of respiratory problems or stress, department officials reported Monday.

Out of the 300-plus firefighters who developed a severe and persistent condition dubbed the World Trade Center cough, about half are still on medical leave or light duty, or are awaiting evaluations for disability retirement.

In all, about 500 firefighters might eventually retire on disability because of respiratory problems, said Dr. David Prezant, the department's deputy chief medical officer. That is about 4 percent of the city's 11,500 firefighters.

He spoke in a telephone briefing arranged by the national Centers for Disease Control and Prevention, which is publishing a report by him and colleagues in a special Sept. 11 issue of its Morbidity and Mortality Weekly Report.

In the publication, Prezant and colleagues said that as of Aug. 28, 358 firefighters and five department paramedics were on medical leave or light duty because of respiratory illness that appeared after the trade-center attacks. A total of 250 were on leave with stress-related problems. Those numbers include 37 workers with both respiratory and stress problems.

The World Trade Center cough, which includes coughing, wheezing and shortness of breath, was defined for the study as requiring at least four straight weeks of medical leave. Within six months of the attack, it appeared in 332 firefighters and one paramedic; with treatment, about half have recovered and returned to full duty, Prezant said.

He said he expected a higher recovery rate based on previous experience with smoke inhalation, where the level is closer to 90 percent, he said.

Asked why the cough recovery rate is lower, he said it is not known what firefighters were exposed to last Sept. 11 but that tiny particles in the huge dust cloud could have been be highly dangerous if inhaled. The volume of particles and lengthy exposure over days probably sets the trade-center experience apart from ordinary firefighter exposures, he said.