CANONSBURG, Pa. — Jeb Bush, keen to establish himself as the most policy-focused candidate in the Republican field amid a slide in the polls, introduced a package of energy proposals here on Tuesday, calling for the repeal of a four-decade ban on crude oil exports.

Speaking before employees of Rice Energy, with supporters seated on the flatbeds of two well-placed pickup trucks beside him, Mr. Bush also assailed President Obama and Hillary Rodham Clinton for opposing the Keystone XL pipeline, among other positions likely to be popular with the conservative base.

“Where’s the marching band, for crying out loud?” he said, accusing “radical environmentalists” of demonizing businesses like Rice, a natural gas and oil company. “This is what we should be doing.”

Mr. Bush’s discussion of crude oil exports seeks to inject a roiling congressional debate into the presidential race. Several Republicans in the House have pressed to repeal the ban, an effort that has been championed by the oil industry and has drawn the ire of environmental groups. Though other candidates, including Senator Ted Cruz of Texas, have expressed support for a repeal, the issue has not resonated on the campaign trail.