Nearly two-thirds of the children, who were chosen because they enjoyed adequate diets and excellent health care, had excessive inflation of their lungs.

Both conditions are associated with high levels of ozone and particulate matter in the air, according to a team of investigators led by Lilian Calderon-Garciduenas of the National Institute of Pediatrics in Mexico City and Lynn Ansley Fordham of the University of North Carolina in Chapel Hill.

By comparison, lung abnormalities were significantly less common among 19 children living in a small coastal town, they said in a report presented to a meeting of the Radiological Society of North America. The scientists said their expectation was that all the children would have normal chest X-rays.

Twenty-five children with the most abnormal X-rays also underwent computerized tomography scans that showed 10 had mild thickening of the walls of bronchial air passages, eight had trapped air in their lungs, four had unusually prominent central airways, and one child had a lung nodule.