After Congress reconvenes Jan. 4, Americans had better brace themselves for some substantial changes in this nation's environmental laws.

Up to a point, the changes promised by the new Republican majority in the legislative branch of government are entirely in order. Much of the red tape generated in the name of clean air and water is too complicated and stifling for business and, consequently, too costly for consumers. Likewise, many of the costs to government have been passed along by Washington to state and local governments.But before the next Congress decides just how far and fast to go in overhauling environmental laws, the lawmakers ought to take a close look on some new scientific findings about the impact of pollution - particularly air pollution.

Those findings were outlined a few days ago at a symposium sponsored by the National Association of Physicians for the Environment and the National Institute of Environmental Health Sciences. The bottom line is that air pollution hurts in more ways than were previously known. Besides harming the lungs, dirty air also impairs the nerves, kidneys, reproductive system, skin and bones.

Among the specific findings are these startling conclusions:

- Hundreds of chemicals found in the air attack the nervous system and contribute to psychological disorders ranging from insomnia to depression.

- Some air pollutants can lower the sperm count in males, leading to reduced fertility or sterility.

- Metals and other compounds taken in through the lungs can be stored in the bones and released during periods of physical change, including pregnancy and menopause.

- Children are particularly at risk because they spend more time outdoors, they tend to breathe through the mouth rather than the air-cleaners of the nose, and they take in more air as a result of physical exertion.

- The delayed effects of air pollution can be especially hard on women because they live an average of seven years longer than men and a large part of that last seven years is spent with chronic diseases.

One final point of fact: Many public opinion polls show most Americans still believe the government has an obligation to protect the environment.

All things considered, the next Congress should look on the results of the Nov. 8 elections as a mandate to reform the environmental laws, not an excuse to undertake a wholesale dismantling.