New York ? Six months after Sept. 11, more than a quarter of New York City’s public school children had at least one anxiety disorder, with almost 15 percent suffering from agoraphobia — a fear of being in public spaces where escape is difficult.

About 12 percent suffered from separation anxiety — fear of being away from one’s parents and family — and a little more than 10 percent suffered post-traumatic stress disorder, according to a study of a representative sample of schoolchildren in grades 4 through 12.

The study was carried out by a team led by Christina W. Hoven, an assistant professor at Columbia University Medical Center and director of epidemiology at Columbia’s Mailman School of Public Health.

The study of 8,236 children found that 28.6 percent had an anxiety disorder six months after the attacks. If applied to the entire population of New York City children in grades 4-12, that figure translates into 204,829 school children suffering an anxiety disorder after Sept. 11. These are internalized disorders, difficult for even an attentive parent or teacher to detect, Hoven said.

“You can’t tell by just looking at a child that the child is having stomach aches or nightmares, or not sleeping at night or having thoughts of suicide,” Hoven said, adding her study is a cry for routine mental health screening. “There is a need for systematic screening and assessment.”

Preliminary findings were made public in 2002, but the paper is being published for the first time in the May issue of Archives of General Psychiatry.

Surprisingly, children who attended schools closest to Ground Zero were at lower risk of anxiety disorder, while risk was elevated among children who had experienced another traumatic event before Sept. 11, or whose parents were involved in the World Trade Center, even if unharmed.

Girls and children in the fourth and fifth grades were more likely to have developed an anxiety disorder, as were children who were repeatedly exposed to media coverage of the World Trade Center attacks, the study found.

The three most common disorders found were agoraphobia, separation anxiety and PTSD, and these three generally occurred at more than triple the normal rate.

One reason children who attended school near Ground Zero seemed to have fewer emotional problems may have been because of the plethora of support services provided in the aftermath, Hoven said.