(AP) — Democratic presidential candidate Sen. Barack Obama and two of his Illinois colleagues are urging the U.S. Environmental Protection Agency to mount a "comprehensive" review of proposed air and construction permits for BP's Whiting refinery.

Obama and fellow Illinois Democrats Sen. Dick Durbin and Rep. Rahm Emanuel suggest that Indiana is rushing the permit process for the refinery, which BP plans to expand into a hub for processing heavy Canadian crude oil.

They raised their concerns in a letter sent Tuesday to the EPA's Chicago office which states that the Indiana Department of Environmental Management has "set an aggressive timeline to issue a final permit" for the refinery about 20 miles southeast of Chicago.

"While it is certainly possible to make determinations on the impact of significant plant modifications to regulated air quality standards and to do so in a compressed timeframe, a thorough EPA review of IDEM's decisions is clearly merited," their letter states.

The congressmen also said they had questions about whether the two draft permits that IDEM released earlier this month comply with Clean Air Act requirements.

One of BP's proposed permits details the construction changes the refinery would undergo as part of the $3.8 billion expansion. The other sets the proposed new pollution emission levels the expanded refinery would have to meet.

The congressmen's letter expresses concern that the two permits combine the "authority to construct with authority to operate."

Their letter follows last summer's uproar over a wastewater permit that IDEM granted to BP that allows the company to increase pollution discharges into Lake Michigan. That permit sparked weeks of criticism from environmentalists who said the permit amounted to a reversal of decades-long efforts to reduce pollution in the lake.

In August, BP said it would either find a way to stay within the discharge limits set for ammonia and suspended solids in its previous discharge permit or drop the expansion plans.

EPA spokesman John Mooney said Wednesday that the agency's regional office in Chicago has been working for months with Indiana regulators on the draft air and construction permits.

"The fundamental role we'll play here is ensuring that these permits do meet the requirements of the Clear Air Act and that public health is being protected," Mooney said.

He said the agency is preparing a reply to Obama, Durbin and Emanuel about the questions raised in their letter.

Mooney said that the EPA would release its comments on IDEM's proposed BP permits during Indiana's public comment period for the documents. That comment period runs through March 21.

IDEM said in a statement Wednesday that it "welcomes the opportunity to receive constructive comments about the draft BP air permits." It also noted that it recently extended the public comment period for the permits and moved a public hearing on them from Feb. 25 to March 14.

Environmental activists have greeted those extensions, saying it will give them more time to review the permits, both of which run about 1,370 pages each and are highly technical.

IDEM has said that it expects the 1,400-acre refinery's air emissions to drop due to equipment upgrades planned as part of the expansion.