WASHINGTON (Reuters) - President Barack Obama intends to nominate air quality expert Gina McCarthy to lead the U.S. Environmental Protection Agency and nuclear physicist Ernest Moniz to head the Department of Energy as early as this week, according to a source familiar with the process.

McCarthy, currently the assistant administrator for the EPA Office of Air and Radiation, was the leading candidate for the job to replace EPA chief Lisa Jackson, who stepped down this month.

Moniz, a former undersecretary of energy during the Clinton administration, is director of the Massachusetts Institute of Technology's Energy Initiative, a research group that gets funding from industry heavyweights including BP, Chevron, and Saudi Aramco for academic work on projects aimed at reducing greenhouse gases.

He would replace Steven Chu, a Nobel Prize-winning physicist, who is stepping down.

(Reporting by Jeff Mason; Editing by Bill Trott)