INDIANAPOLIS (AP) — Federal regulators have found no significant problems with a proposed air permit for BP's planned expansion of its Whiting oil refinery — a permit the company hopes to get approved before emission credits it earned years ago expire.

In its March 21 letter to Indiana officials, the U.S. Environmental Protection Agency lists six areas in the draft air and construction permits released in February by the Indiana Department of Environmental Management that need clarified or additional support data.

Environmental groups who contend that those proposed permits do not comply with the Clean Air Act have said they may sue to try to prevent them from taking effect.

But John Mooney, an air pollution expert at the EPA's Chicago office, said the agency conducted a "fairly extensive review" of both proposed permits and found no evidence that either document would not meet the federal law.

Still, he said it's premature to say whether the agency will approve the permits.

"It's too soon to tell — too much can change at this point in the process. But obviously, the version we saw looked pretty good," Mooney said Thursday.

He said the EPA will now await IDEM's response to the issues the EPA raised in its letter, and will also review Indiana's responses to comments it received from environmental groups and the public on the permits, each of which runs more than 1,300 pages.

Ann Alexander, a senior attorney with the Chicago-based Natural Resources Defense Council, said she's not surprised by the EPA's conclusions on the draft permits. She said the EPA has failed to do more to protect air quality in the greater Chicago metropolitan area.

"EPA is patching little holes in the fence when they left the front gate wide open," Alexander said Thursday in e-mailed comments.

In a 200-page technical and legal commentary sent to IDEM on the draft permits, the Natural Resources Defense Council and other environmental groups that concur with its analysis detailed what they called several deficiencies in the permits.

Among those, they said the proposed air permit's analysis of the expanded refinery's emissions fails to take into account all of the expected emissions from three new flares that would be added. Those tall chimney-like structures burn off waste substances.

Company officials hope to have the permits approved before June 1, when air emission credits the refinery received for improvements it made in 2003 will expire.

Those and other emissions credits BP has earned would allow the company to offset some emissions from the expanded refinery, which would become a hub for processing heavy Canadian crude oil.

With those credits and planned equipment upgrades, BP has said the refinery's net emissions would decrease when the expansion goes online in 2011, even though particulate matter and sulfur dioxide emissions would increase.

If emissions at expanded industrial operations rise above a certain threshold it is deemed a "major modification," and the EPA can require companies to install additional pollution control devices or take other steps to reduce emissions.

Mooney said the draft permits indicate the changes planned for the Whiting refinery do not meet the "major modification" criteria, and therefore extra emission controls won't be needed.

Environmentalists are concerned that a significant increase in carbon dioxide, a greenhouse gas, at the expanded refinery about 20 miles southeast of Chicago will add to global warming.

Last April, the U.S. Supreme Court ruled that carbon dioxide from burning fossil fuels is a pollutant subject to the Clean Air Act and directed the EPA to determine if CO2 emissions endanger public health and welfare.

"Given the recent Supreme Court decision, we are confident this issue must be addressed," said Tom Anderson, the executive director of the Michigan City-based Save the Dunes Council.

IDEM held a public hearing on the draft permits March 14 in Hammond. On Thursday, nine members of Illinois' congressional delegation asked the EPA's Chicago office to schedule a public hearing on the permits in Illinois.

"The people of Illinois, who will also be directly affected by this permit, have not had an opportunity to weigh in on this decision ... ," their letter to the EPA states.