Speculation is mounting that outgoing EPA chief Lisa Jackson will be replaced by Gina McCarthy, the EPA’s assistant administrator for air and radiation for the past four years.

Known as President Obama's "green quarterback," McCarthy has three decades worth of experience in working on environmental regulations at the state and federal level, and was instrumental in writing roles regulating power-plant emissions during Obama’s first term.

McCarthy worked as a health and environmental-protection official in Massachusetts for 25 years, serving under five governors representing both parties, including Mitt Romney, who tasked her with authoring a state climate-change plan. She then went on to head Connecticut’s EPA for five years.

McCarthy has received support from both environmentalists. Due to her willingness to reach out to industries while developing regulations, she has also – surprisingly — gotten grudging respect from those not usually known for their fondness for the EPA, such as coal-fired electric utilities and automakers.

However, if nominated, McCarthy will probably face stiff opposition from Republicans on the Senate Environment and Public Works Committee. The panel’s ranking Republican, Sen. David Vitter of Louisiana, and senior Republican member John Barrasso of Wyoming hail from oil- and coal-producing states where EPA regulations are viewed as job-killers.

Vitter has already launched a public campaign of sorts against McCarthy, questioning the scientific methods used in EPA’s regulatory agenda. And in 2009, Barrasso initially blocked McCarthy’s nomination to her current slot at EPA, in part because of concerns about her approach to regulating greenhouse gases that cause climate change.

Last summer, EPA released an ambitious new regulation that will dramatically increase fuel efficiency in cars and trucks, the strongest action the Obama administration has taken so far to fight climate change—but one that required lengthy negotiations with automakers.

“She’s a pragmatic policymaker,” said Gloria Berquist, vice president of the Alliance of Automobile Manufacturers. “She has aspirational environmental goals, but she accepts real-world economics.”

The coal industry and coal-fired power plants will feel the biggest economic pinch from EPA regulations on greenhouse gases. American Electric Power, an Ohio-based electric utility with a fleet of generators that depends heavily on coal, protested the Obama administration’s first-term clean-air rules and is deeply concerned about coming climate rules.

But officials in that company say that McCarthy heard them out. “Early on, Gina brought us in to talk about the rules,” said John McManus, AEP’s vice president of environmental services. “We talked about timing, technology, and cost. My sense is that Gina is listening, has an open mind, she wants to hear the concerns of the regulated sector.”

AEP told McCarthy that a rule aimed at cutting soot emissions was so stringent that it would cripple the company. Eventually, McCarthy agreed to loosen a portion of the rule—a move that saved the company about 10 percent of the cost of meeting the rule's requirements.

McCarthy has drawn the ire of some allies in the environmental community for her industry outreach. But, ultimately, they say her approach is likely to lead to realistic rules that will stand up to challenges by industry.

“She gives a lot of tough love,” said William Becker, head of the National Association of Clean Air Agencies. “And those in the environmental community understand and welcome the truth. If you explain what you’re thinking and what’s causing you to make that conclusion and you do it in a professional and nice way, that tends to deflate a lot of the aggression. She’s brutally honest, very fair, humorous, and an incredibly hard worker. She’s not an ideologue. She’s a practitioner.”