WASHINGTON – EPA Administrator Lisa P. Jackson said Thursday she is stepping down from the Cabinet-level post after four years in which she won new federal regulations for carbon dioxide emissions but also sparred often in bitter partisan fights with Republican lawmakers and industry executives.

The first African-American to hold the position, and a chemical engineer by training, Jackson gave no signal on what she plans to do next. But sources close to Jackson, 50, hinted that she may be headed back to her former home in New Jersey, either for a chance to become president of Princeton University or to run for governor.

Reaction was largely muted among industry leaders and Republican lawmakers, as they instead viewed the opening at the Environmental Protection Agency as a rare opportunity to push back on many regulatory policies they see as intrusive and harmful to the stumbling economy.