A coal-fired power plant just across the Delaware River in Pennsylvania has been spewing tons of pollutants into New Jersey's air for years while the state's own coal plants have been forced to clean up their emissions.

Now, New Jersey's long battle to compel the plant to install cleaner technology may yield some results. The U.S. Environmental Protection Agency will schedule a hearing early next year to discuss whether the plant should be forced to reduce its emissions.

North Jersey continually fails federal clean air standards, in part because it is downwind of coal-burning power plants in Ohio, western Pennsylvania, and other places. State officials blame the emissions for contributing to New Jersey's high asthma rates and other health problems.

GenOn Energy's plant in Portland, Pa., emitted 30,000 tons of sulfur dioxide last year - almost three times the amount of all seven of New Jersey's coal plants combined. It is on the banks of the Delaware across from Warren County.

"There is no power plant that impacts New Jersey more than this one," said Bill O'Sullivan, head of the state Department of Environmental Protection's air quality program. "It's a serious problem because it's so close."

A spokesman for the company, known as RRI Energy before a merger this month, would not answer questions and released a statement saying the Portland plant complies with all permit limitations issued by the Pennsylvania Department of Environmental Protection.

"We are aware that expected future rules will be even more restrictive than today's permit standards, and fully intend to take the necessary steps to comply with future rules as they are developed and become effective," the statement reads.

The New Jersey DEP's air monitors and computer models have shown that sulfur dioxide from the plant has wafted into Warren, Sussex, Hunterdon and Morris Counties. O'Sullivan said it was likely that it also pollutes air in Passaic and Bergen Counties.

"We have a monitor in Chester that shows spikes of sulfur dioxide" whenever the wind blows from the west, O'Sullivan said. "There is no doubt that it spreads beyond that. This plant affects all of northeastern New Jersey."

New Jersey DEP officials have long argued that the plant is violating federal regulations by not installing modern pollution control equipment whenever it makes upgrades to increase production. The DEP sued the EPA in 2006 for not enforcing those regulations at the plant. A year later, the DEP sued RRI.

In May, the DEP petitioned the EPA arguing that the plant, built in the 1950s and 1960s, has outdated controls for particulate matter and no emission controls for sulfur dioxide, which burns the respiratory tract and can have serious health consequences for people with lung disease.

The EPA said it was investigating the matter and would issue its findings in February. A hearing will be held soon after. DEP officials want that hearing in Warren County.

The EPA is headed by Lisa Jackson, the former commissioner of the state DEP, which sued the plant in 2007.

Making emissions cleaner is costly. Public Service Electric & Gas has spent more than $1 billion upgrading its two coal plants - one in Jersey City, the other outside Trenton - to dramatically cut down on the toxic substances that leave its smokestacks every day.

Emissions of nitrogen oxide, sulfur dioxide, particulate matter, and mercury are expected to be reduced by 85 percent to 93 percent at the Jersey City plant. The plant released 176,000 pounds of toxic chemicals into the air in 2009, down from 1.5 million in 2007, according to data released by the EPA this month. Still, it was 34,000 pounds more than the combined toxic emissions from all businesses in Bergen and Passaic Counties.

A company has proposed building a coal-burning plant in Linden. Developers have said the plant would use the newest technology available to curb emissions. It would also have a "carbon capture" process, where carbon dioxide generated from the PurGen plant would be pumped through a pipeline into rock formations beneath the ocean, about 70 miles off the Atlantic City coast. Critics have contended that the safety of the process remains unproven, and the company, SCS Energy L.L,C,, has argued otherwise.

The DEP is awaiting a new application for an air permit for the PurGen plant, a spokesman said. During his 2009 campaign, Gov. Christie said he opposed the project despite assurances from the company.

In recent years, New Jersey has filed many lawsuits to force coal-burning plants and the federal government to cut air emissions.

A report from the advocacy group Clean Air Task Force says pollution from coal-burning power plants will cause 531 deaths in New Jersey this year.

Still, the number of deaths nationwide was almost halved to 13,200 from an estimated 24,000 in 2004, according to researchers who analyzed statistics from the EPA.