Gina McCarthy, assistant administrator for EPA’s Office of Air and Radiation, at a House hearing. (Melina Mara/The Washington Post)

Looks like the field of candidates to head the Environmental Protection Agency is narrowing — perhaps even down to one name: Gina McCarthy, now the assistant administrator for the agency’s Office of Air and Radiation, according to people familiar with the White House’s selection process.

McCarthy is the leading contender to be President Obama’s pick to lead the EPA, but no final decision has been made, a development first reported by Reuters. Her name has long been on the list of potential successors to current Administrator Lisa Jackson, who announced in December that she would step down.

Deputy administrator Bob Perciasepe, another name often mentioned as a possible replacement for Jackson, is still “in the mix,” according to Reuters.

Whoever the nominee is, they will likely face tough questions in the Senate, given the political divisiveness of the issues confronting the EPA.