WASHINGTON — The Environmental Protection Agency yesterday lowered the allowable amount of smog-forming ozone in the air to 75 parts per billion, a level significantly higher than what the agency’s scientific advisers had urged for this key component of unhealthy air pollution.

Administrator Stephen Johnson also said he would push Congress to rewrite the nearly 37-year old Clean Air Act to allow regulators to take into consideration the cost and feasibility of controlling pollution when making decisions about air quality, something that is currently prohibited by the law. In 2001, the Supreme Court ruled that the government needed to base the ozone standard strictly on protecting public health, with no regard to cost.

The new smog rules — one of the most important environmental decisions facing the Bush administration in the president’s final year in office — will be a major factor in determining the quality of the air Americans will breathe for at least a decade. The standards, which are aimed at protecting both public health and welfare, are designed to limit the amount of nitrogen oxides and other chemical compounds