NADVOITSY, Far North --The children of this town learn early not to smile.


When they do, they show a ghastly array of blackened, splintered, rotting stumps where milk-white teeth might have been.


An environmental plague has struck this northern land of lakes, no longer pristine, and thinning pine forests. The children of Nadvoitsy are its victims.


Their disease is caused by a pollutant that the town's main employer, the Nadvoitsy Aluminum factory, dumped in its backyard for three decades. Slowly, the contaminant seeped through the soil to the lake that supplies drinking water to almost all the 19,000 residents of this little town near the Finnish border.


In one of the many cruel ironies bred by environmental indifference in the former Soviet Union, the substance that has sickened an estimated 4,000 children in Nadvoitsy is massive quantities of fluoride. Because it is beneficial in small doses, no one ever bothered to check for its presence.


Then, for years after officials discovered the chemical culprit, in the mid-1980s, townspeople continued to drink from the poisoned lake. Building a pipeline to a cleaner water source was deemed too expensive.


Dreadful as Nadvoitsy's story is, its water woes are hardly unique. A new report from the Environment Ministry says half of Russia's population is forced to rely on substandard drinking water.


As this one-factory town and hundreds of other dangerously polluted Russian cities have discovered, environmental safety has become a casualty of the country's economic chaos.


Forty-three Russian cities are in urgent need of air-pollution relief, 1,016 plant and animal species are endangered, and deforestation is widespread, the World Bank reported recently.


Virtually nothing has been done to clean up the radioactive and toxic waste sites littering the country. And as a symbol of the environmental calamities here, even the most basic of human needs -- clean water -- has been put on hold.


Alexei Yablokov, the grand old man of Russia's environmental movement, recently warned that the dreadful ecological legacy of the former Soviet Union has only been worsened by five years of economic decline.


Between 14 and 15 percent of Russian territory is so polluted as to be unsafe for habitation, but 40 million people live there anyway, Yablokov said.


Environmental problems are low on the agenda for a new Russian leadership that has been consumed by simultaneous political, ethnic and economic struggles at home and near its borders.


But while Moscow's mind is elsewhere, ecologists say, Russia's far-flung provinces are being ravaged by uncontrolled strip-mining, clear-cutting of forests and surreptitious dumping of hazardous wastes.


"The term 'ecocide' is very appropriate," Yablokov said.


When Russian authorities do catch environmental despoilers red-handed, they mete out only puny punishment.


In 1993, Nadvoitsy Aluminum spewed out 8,640 tons of pollutants, including airborne fluoride. But it has paid just $3,500 in fines this quarter for exceeding pollution limits, said Valentin Kudryavtsev, the senior environmental inspector who has been tenaciously prodding the aluminum plant and its neighbors to clean up.


Pollutants have seeped into underground aquifers, especially in the intensely industrial European part of Russia, according to the Environment Ministry report. It found the quality of 80 aquifers that supply 60 cities with drinking water had worsened in 1993.


In the cities, aging water-treatment plants are inadequately maintained, and authorities simply add more and more chlorine to counter the rising bacteria.


Where there is industrial equipment to control water pollution, it is often obsolete and overburdened.


More than 20 percent of the drinking-water samples the ministry studied in 1993 flunked biological or chemical purity tests, and 4.3 percent of samples contained such high bacterial counts as to pose "real epidemiological danger." Overall, the report concluded that Russia's drinking water problem is now critical, and "has a dangerous tendency to deteriorate."