WASHINGTON — States and local officials across the country awaited word today on whether they will have to further cut air pollution to protect millions of people, especially the very young and the elderly, from respiratory illnesses.

The Environmental Protection Agency is planning to announce whether it will tighten the federal health standard for ozone, commonly known as smog, and leave several hundred additional counties falling short of what the federal government considers healthy air.

The EPA last year said it was considering lowering the standard from 80 parts per billion of ozone per unit of air to between 70 and 75 parts per billion. In recent weeks a broad range of industry groups have lobbying the EPA and the White House to keep the current standard despite warnings from most health experts that it does not adequately protect public health.

The EPA scheduled a news conference to announce its plans. The agency is under court order to come up with a smog ruling by March 13.

EPA Administrator Stephen Johnson has told members of Congress he is convinced that science shows the current standard, enacted more than a decade ago, must be tightened. But he is not expected to lower it as much as many health experts argue is needed.

An independent EPA advisory group of scientists has urged the agency to adopt an ozone standard of 60 to 70 parts per billion, saying that’s what is needed to provide an adequate margin of protection to millions of people susceptible to respiratory problems, including the very young and elderly. A similar conclusion was reached by a second advisory board on children’s health.

In December, 111 health scientists in a letter to Johnson also urged the EPA to adopt the findings of the science panels.

But industry groups representing manufactures, electric utilities, chemical and oil companies, and other groups have lobbying hard in recent weeks against any change in the federal standard. They argued at the EPA, White House and in Congress that lowering the current requirement would be too costly and threaten the economies of areas that will have impose new pollution controls. They contend the health benefits of lowering the smog standard have yet to be proven.

Health advocates disagree.

“Most studies show a steady reduction in the public health burden as the standard is tightened,” said Jonathan Levy of the Harvard Center of Risk Analysis.

The EPA has said, based on various studies, cutting smog from 80 to 75 parts per billion would prevent between 900 and 1,100 premature deaths a year, 1,400 fewer nonfatal heart attacks and 5,600 fewer hospital or emergency room visits. A separate study suggests that tightening the standard to 70 parts per billion could avoid as many as 3,800 premature deaths nationwide.

The air quality in about 85 of more than 700 counties currently exceeds the federal health standard for smog during at least some days of the year. If the standard is lowered to 75 parts per billion, that number of counties in noncompliance is expected to roughly quadruple, according to the latest EPA estimates.

The EPA by law is not supposed to consider economic cost in establishing the federal health standard for air quality. The agency has estimated new pollution control efforts to comply with a 75 parts per billion standard would be as much as $8.8 billion a year, although acknowledging that does not take into account reductions in health care costs which could be even greater.