While high gasoline prices and global warming fears have set the stage for a sweeping overhaul of U.S. energy policy, Republican presidential candidate John McCain (Ariz.) faces a minefield in implementing key elements of his energy agenda should he prevail over Democratic Sen. Barack Obama (Ill.) in November.

McCain’s positions on climate change and nuclear power, as well as his long-standing opposition to federal support for ethanol, place the Senator on a collision course with his own party as well as Congressional Democrats and a wide swath of rural America.

McCain has long touted his support for fighting global warming through a cap-and-trade program, under which the government sets annual emission limits and issues companies permits that can be traded to meet the levels. While embracing that issue may burnish his reputation as a maverick and win him support from crucial independent voters, the GOP as a whole has shown little enthusiasm for the plan, which many view as a hidden tax.

“I think that a tax-and-regulate model is wrong, and I think it’s not going to pass,” former Speaker Newt Gingrich (R-Ga.) said of McCain’s support for cap-and-trade in an interview last month.

McCain economic adviser Steve Forbes raised eyebrows in July when he likened cap-and-trade to an aborted effort by President Bill Clinton to institute a BTU tax, or levy on the heat content of fuels. “I don’t think those things are going to get very far as people start to examine the details of them,” he told CNN.

But McCain campaign spokesman Taylor Griffin dismissed Forbes’ remarks and reiterated that the Senator is committed to addressing global warming. “That’s Steve Forbes’ view,” he said. Climate change “is a vital problem that must be addressed, and you can expect Sen. McCain to continue to press” cap-and-trade as a solution.

Anti-tax activist Grover Norquist, who heads the group Americans for Tax Reform, is another leading conservative who expressed doubts that cap-and-trade would get very far in a McCain presidency.

“I don’t expect it to be a serious effort in the future,” he said in an interview, noting that McCain did not support a cap-and-trade bill sponsored during this session by his close friend, Sen. Joe Lieberman (ID-Conn.). In addition, he said McCain shares concerns with many conservatives about the wisdom of controlling U.S. greenhouse gas emissions without a similar commitment from nations such as India and China, which are also major greenhouse gas emitters.

“I think [cap-and-trade] is a mistake, and I would hope that at the end of the day, upon reflection, President McCain would see the same challenges,” Norquist said.

Former New Jersey Gov. Christine Todd Whitman (R) disagreed. Whitman — who as the current administration’s first Environmental Protection Agency administrator was famously undercut by President Bush when he backtracked on his campaign pledge to regulate carbon dioxide — predicted that Republicans will come around and support the plan.

“It should be the kind of approach that Republicans should embrace … because it’s market-based,” she said last month.

Whitman said she sees the enactment of a cap-and-trade law in the next two to four years, noting the stated support of both McCain and Obama for the plan. While conceding that Democrats are more likely to provide the votes for passage, “I think he’d get Republicans with him, absolutely,” she said of McCain.

But Congressional Democrats are highly unlikely to embrace another aspect of McCain’s plan to reduce global warming — the building of 45 nuclear reactors by 2030 by taking steps to “smooth the regulatory process,” Griffin said.

Whitman, who co-chairs the pro-nuclear Clean and Safe Energy Coalition, said the permitting process for new plants has already been streamlined, making further changes a tough sell. “You have to hold the nuclear industry to high standards,” she said.

And while nuclear energy does not produce greenhouse gases, many Democrats remain concerned over how to permanently store highly radioactive nuclear waste, as well as the risks of proliferation of nuclear technology.

McCain’s support for the proposed nuclear waste repository at Yucca Mountain, Nev., poses another stumbling block. The controversial project has been hamstrung for years by litigation, regulatory hurdles and budget woes, and while supporters have proposed legislation to expedite its completion, such bills are unlikely to advance as long as Sen. Harry Reid (D-Nev.) — a fierce Yucca opponent — remains Majority Leader.

McCain has also called for a national debate on the reprocessing of nuclear waste, a controversial and expensive idea backed by the Bush administration that failed to gain much traction even when pro-nuclear Republicans controlled Congress.

On another simmering energy issue, McCain’s long-standing opposition to federal subsidies and mandates for ethanol could alienate rural voters.

McCain was among the dozens of Congressional Republicans who pressed the EPA earlier this year to reduce the quantity of biofuels like ethanol that is required to be blended into gasoline. The federal mandate, which is popular in states that grow corn for ethanol, is blamed by critics for contributing to higher global food prices by nudging farmers to grow crops destined for gas tanks instead of dinner tables.

The EPA rejected the request last month, but the food-vs.-fuel debate is far from over. Members of both parties are lining up on either side of the issue, reflecting the regional, rather than partisan, nature of the debate. McCain, if he became president, would be a powerful ally for those in Congress who would like to scale back support for ethanol.

If elected president, Griffin said, McCain would work to eliminate a federal production tax credit for corn-based ethanol, as well as an import tariff that is credited with keeping cheap Brazilian ethanol out of the United States.

However, he also noted that McCain would consider shifting some existing subsidies for corn-based ethanol toward other alternative fuels, such as cellulosic ethanol, an experimental fuel that could in theory be produced from nearly any plant material.

Whitman said she fully expects McCain as president to follow through on his long-standing opposition to ethanol subsidies, despite the political risks.

“Every time you try to get something done in the farm bill that cuts back on that, then you run into that buzz saw of a very powerful lobby,” she said. “But I do think that John McCain is someone who’s willing to take that on. And if anyone can get it done, he would be the one.”

Meanwhile, McCain and his running mate, Alaska Gov. Sarah Palin, disagree on whether to drill in the Arctic National Wildlife Refuge. He has long opposed it; she aggressively backs it.