Washington ? Christie Whitman resigned as Environmental Protection Agency administrator on Wednesday, weary after two and a half years of struggles with fellow Bush officials, Congress and business and environmental groups.

“Halfway through last December, I was … saying ‘Do I really want to live this lifestyle for another two and a half years?’ It was pretty apparent I didn’t,” she told reporters.

Whitman, who differed with the White House on issues ranging from global warming to power plant pollution, informed President Bush of her decision during a half-hour meeting in the Oval Office on Tuesday afternoon.

She told the president that she considered her tenure at the EPA rewarding professionally, but that it was time to return to her home and husband in New Jersey.

“I said, ‘It’s time to go. He said, ‘I know,”‘ Whitman said. She plans to step down on June 27.

With Whitman’s departure, Bush loses one of the most prominent women in his Cabinet — a moderate former New Jersey governor selected by the president to help soften his image as a political conservative, particularly on environmental issues.

White House officials, who sought to deflect any suggestion Whitman had been forced out, said it would be weeks before a replacement would be named.

The president will be under pressure to appoint someone acceptable to his conservative GOP supporters and the business community, but not alienate moderate Republicans and swing voters who favor increased environmental protection.

Whitman’s departure is an “opportunity for revolution” if Bush appoints a successor inclined toward less regulation, said the conservative Competitive Enterprise Institute.

But Fred Krupp, president of Environmental Defense, said the next EPA administrator “must be an independent voice for public health and the environment” in a Cabinet already heavily leaning toward business interests.

Meeting with reporters, Whitman cited as accomplishments: reducing pollution from off-road diesel engines; restoring low-level pollution sites known as “brownfields;” a push to cut pollution from school buses; a number of pollution-reduction settlements with industry.

Addressing her differences with the White House, Whitman said, “I wouldn’t characterize them as conflicts. I mean, dynamic discussions, yes. But that’s what happens all the time.”

Whitman clashed with senior White House officials and others in the administration over how best to address climate change, arsenic levels in drinking water, and industry complaints that EPA’s air pollution rules were stymieing efficiency improvements.

Whitman joined the administration after seven years as governor of New Jersey, where she made preservation a priority but never managed to convince environmentalists she was one of them.