A government cancer expert said yesterday that a Japanese researcher was in error last fall when he reported that fiberglass exposure caused a precancerous lung problem in a female factory worker.

Dr. Margaret H. Sloan, of the National Cancer Institute, said the report that was delivered at NCI last Nov. 15 by Dr. Tatsuo Sano did not take into account the fiberglass worker's exposure 30 years ago to asbestors. Asbestos is regarded by most medical experts as a potent carcinogen with a long latency period.

"It now appears it is quite possible to explain this case as exposure to asbestos," Sloan said. She said other workers in the factory in Japan where the woman worked were examined and none was found to have similar lung problems.

Sloan said the cancer institute was preparing a bulletin announcing the new information.

Sano, who is vice director of the Institute for Science of Labor, Environmental and Occupational Disease in Kawasaki, set off concern among both the medical and industrial communities with his report. U.S. firms annually produce billions of pounds of fiberglass which is widely used in home and building insulation.

In February two medical experts were sent to Japan to check on Sano's findings, which also included a report that six other workers besides the woman who were employed in a small fiberglass fabricating plant had shown lung problems.

The woman, Sano reported, showed a thickening of her lung wall along with a buildup of calcification, or plaque, on the lung lining.

Cancer experts said the condition is usually linked to the development of a rare type of lung lining cancer known as mesothelioma. The disease had only been known to be caused by exposure to asbestos, according to the experts.

What was of particular concern in Sano's report, said cancer specialist, was the fact that he found no asbestos exposure in the woman's history. That raised the possibility that, for the first time, fiberglass may have caused the rare disease.

However, the woman's history was rechecked, Sloan said, and she was found to have had apparent asbestor exposure in two previous jobs she held 30 years ago. A re-examination of her lungs also turned up substantial amounts of asbestos fibers along with glass dust and particle, Sloan said.