COLUMBUS, Ohio (AP) – The nation’s largest power generator broke clean air rules when it failed to cut emissions at a plants in four states that foul the air in the Northeast and can make breathing more difficult, a federal lawyer said Wednesday.

The case against Columbus-based American Electric Power that got started in federal court is the biggest among several filed in the waning days of the Clinton administration against utilities in the Midwest and South.

The government and eight states, including Connecticut, say AEP’s refusal to install new pollution controls means the nine coal-fired plants continue to spew sulfur dioxide, nitrogen oxide and soot that cause acid rain, smog and haze downwind from Ohio. The government says the pollutants lead to severe respiratory problems, including asthma and bronchitis.

Connecticut Attorney General Richard Blumenthal said the plants are a concern for states throughout the Northeast.

“Our air quality depends on the prevailing winds as well as compliance with the laws,” he said.

An attorney from Blumenthal’s office is in Ohio working on the case.

“The plaintiffs expect to establish that AEP’s conduct has resulted in environmental harm,” Leslie Bellas, an attorney with the government’s environmental enforcement section, said in opening statements.

AEP and the utilities have argued that the work done on the plants was routine maintenance, which doesn’t trigger the requirements for expensive pollution controls.

AEP could be required to pay billions of dollars for pollution controls and millions of dollars in penalties if it broke the Clean Air Act.

The work done at the plants was common throughout the company and the industry, AEP lawyer Mike Miller said.

“We will show that completion of projects like those here do not necessarily translate into increased generation or emissions,” he said.

Bellas said that the modifications extended the life expectancy of the plants built in the 1950s and 60s from 35 or 40 years to 50 or 60 years. The changes also made the plants more efficient so they could produce more electricity, which increased pollution, she said.

U.S. District Judge Edmund Sargus, hearing the case without a jury, ruled for the government in the first case to go to trial against Ohio Edison’s W.H. Sammis plant in eastern Ohio. The company, owned by Akron-based FirstEnergy, later agreed to pay $1.1 billion on equipment to control emissions at Sammis and three other plants and $33.5 million in fines and environmental initiatives.

The Bush administration in 2002 and 2003 rewrote the EPA regulations that Clinton used to sue the utilities. Those new regulations have been placed on hold while federal courts review challenges to them.

Even so, Justice Department officials have continued during the Bush presidency to sue utilities.

The government has settled nine cases against power generators that it says will reduce emissions by 940,000 tons a year through the installation of $5.5 billion worth of pollution controls.

Besides Connecticut, the states suing AEP are New York, New Jersey, Massachusetts, Vermont, New Hampshire, Rhode Island and Maryland.

AEP has more than 5 million customers in 11 states. Its nine plants on trial are Muskingum River, Cardinal and Conesville in Ohio; Tanners Creek in Indiana; Amos, Kammer, Mitchell and Sporn in West Virginia; and Clinch River in Virginia. This case involves more plants than any of the lawsuits.

The trial is expected to last about a week. It is not clear when Sargus will rule.