BEIJING - Smog caused by widespread use of low-grade coal has caused more than 45 million Chinese to be affected by fluoride poisoning, an official report said Thursday.

Flourosis, overexposure to flouride, is endemic in practically all Chinese communities. A recent conference of medical workers in Beijing reported that since 1986, only 4 million people have benefited from treatment and prevention programs, the China Daily said.

Fluoride poisoning causes tooth staining and corrosion. In its most severe form, it can cause paralysis.

The high fluoride content of the coal used by many Chinese households for cooking and heating is a major problem. Many water sources also contain dangerously high levels of the chemical.

The report said that more than 100 million people were threatened by the disease. Official records show that 42.88 million Chinese have dental fluorosis, while another 2.37 million have contracted skeletal fluorosis.

''China has the world's most severe problem with endemic fluorosis,'' Chen Junsheng, a member of China's State Council, was quoted as saying. ''It will take a long time to get rid of fluorosis.''

Although China's major cities, like Beijing and Shanghai, are gradually replacing coal-fueled cookers and heaters with gas-run appliances, in other areas pollution has grown worse in recent years. The problem is worst in northern China, the report said.

The government is trying to minimize the problem by changing water sources for some communities and by supplying specially designed stoves to cut down on air pollution, it added.