WASHINGTON – EPA Administrator Lisa Jackson, the Obama administration's chief environmental watchdog, is stepping down after nearly four years marked by high-profile brawls over global warming pollution, the Keystone XL oil pipeline, new controls on coal-fired plants and several other hot-button issues that affect the nation's economy and people's health.

Jackson constantly found herself caught between administration pledges to solve thorny environmental problems and steady resistance from Republicans and industrial groups who complained that the agency's rules destroyed jobs and made it harder for American companies to compete internationally.

The GOP chairman of the House Energy and Commerce Committee, Rep. Fred Upton of Michigan, said last year that Jackson would need her own parking spot at the Capitol because he planned to bring her in so frequently for questioning. Republican presidential nominee Mitt Romney called for her firing, a stance that had little downside during the GOP primary.