An estimated 50 million Americans live in areas where non-cancer health risks from toxic air pollution - such as nerve damage or birth defects - are possible, according to a federal study released Thursday.

While most health analyses have focused on the cancer threat posed by toxic air pollution, the new Environmental Protection Agency study found the potential for non-cancer health effects also was substantial.In looking at 143 toxic air pollutants at 5,000 industrial facilities or monitoring sites nationwide, the study said 54 chemicals were present at concentrations high enough to present a risk of non-cancer health effects.

In addition, the study found 22 pollutants - including benzene, beryllium and chloroform - were at health-threatening levels at more than 25 percent of the 5,000 sites studied.

And in terms of the possible scope of the problem, the study estimated that 50 million people lived within 6 miles of study sites where there were potentially dangerous chemical concentrations.

"The bottom line of this study is that cancer is not the only serious health threat from toxic air pollution," said Beth Hassett-Sipple, lead author of the study and an environmental health scientist with the EPA's Office of Air Quality Planning and Standards. "We have to broaden our perspective to look more carefully at non-cancer health risks."

Hassett-Sipple said the study's conclusions were limited in that little data was available to determine what chemical concentrations were sufficient to cause non-cancer effects in humans. She said her study extrapolated from animal studies in setting possible levels of concern for humans.

Hassett-Sipple said recent studies had indicated her calculations may have slightly exaggerated non-cancer risks to humans.

At the same time, she said her study looked only at industrial emissions of toxic chemicals and did not include pollution from cars - a major source of air toxics.

Hassett-Sipple's study was based on data collected from 1980 to 1988 at 1,500 sites and estimated average annual toxic air pollutant concentrations at 3,500 factories or commercial facilities nationwide.

While not yet formally released by the EPA, the study was disclosed in a weekly health report released by the federal Centers for Disease Control in Atlanta.

The new Clean Air Act passed by Congress last year requires the EPA to issue regulations reducing emissions of 189 common toxic air pollutants discharged by industrial facilities. To date, the EPA has limits on only eight toxic air pollutants.

Federal officials estimate the expanded regulations will prevent thousands of cancer cases each year. However, they have made no projections about their possible impact on non-cancer health effects.