Oil prices flirting with $100 a barrel, warnings of climate change and holiday road trips fueled by gas topping $3 a gallon are combining to give energy issues unprecedented prominence in the presidential campaign.

"The bottom line for us, we're happy everybody is talking about it," said David Willett, national press secretary for the Sierra Club. "Even in '04, while there was a clear difference between the candidates, it wasn't really a campaign issue."

The Republicans, with notable exceptions, have concentrated on the dangers to the nation's strategic and economic security of relying on energy from the Middle East.

The Democrats, while embracing those same arguments, have placed much greater emphasis on the threat of global warming.

"The positions the leading Democratic candidates have advanced are, for the most part, very thoughtful, very much at the strong end of realistic," said Manik Roy, director of congressional affairs for the Pew Center on Global Climate change. "I'm not seeing as much from the Republican candidates."

A New York Times survey of likely caucus and primary voters in Iowa and New Hampshire, for example, found that Democrats were significantly more likely to cite the environment as a primary issue in choosing a candidate. Mr. Roy emphasized, however, that Republican Sen. John McCain of Arizona stood out from the GOP field in his emphasis on global warming.

Mr. Roy pointed to the senator's work with Sen. Joseph Lieberman, D-Conn., in pushing, unsuccessfully so far, for legislation that would cap the overall levels of greenhouse gas emissions in tandem with a system in which emitters could buy and sell permits authorizing the release of different levels of the targeted pollutants.

"He completely changed the dialogue in the Senate, and, to a certain, extent, in the House," Mr. Roy said.

Variations of the cap-and trade proposal are also central to the energy plans offered by the leading Democratic candidates. They also tend to favor greater or complete reliance on an auction system for distributing the emission permits, as opposed to one in which certain industries, such as existing coal-fired plants, are granted some level of emission allowance by the government.

Sens. Hillary Rodham Clinton, D-N.Y. and Barack Obama, D-Ill. and former Sen. John Edwards of North Carolina would use part of the proceeds of the cap-and-trade auction to fund research on advances in renewable energy, clean-coal technology and similar efforts. The leading Democrats also propose to fund energy research by curtailing a variety of tax breaks for major oil companies.

Sen. Christopher J. Dodd, D-Conn., stands out among the candidates for his call for a broader carbon tax on corporations of all kinds. Despite their generalized calls for conservation, none of the candidates has supported significantly higher fuel taxes, along the European model, to hold down consumption.

Alternative energy

The politics of climate change have produced what once would have been considered strange bedfellows. With the exception of U.S. Rep. Dennis Kucinich, D-Ohio, who calls for a gradual phase-out of both nuclear and coal-fired plants, all of the candidates at least acknowledge the need for nuclear power as part of the nation's energy future, a position that once would have been anathema to Democratic primary voters.

"When you look at their comments in general, particularly the leaders, they realize that nuclear has to play a significant role," said Mitch Singer, a spokesman for the Nuclear Power Institute, an industry lobbying group. "These are not dumb people. They are aware of the fact that the demand for energy is expected to grow by 40 percent by 2030."

The Democrats' difficulty with the implications of nuclear power generation were evident, however, at their debate in mid-month in Las Vegas. The candidates were united in their opposition to the opening of a federal facility for storing spent nuclear fuel at Nevada's Yucca Mountain, undeterred by the fact that several of them had supported the facility in the past. And despite their opposition to that site and their grudging support for expansion of the plants that produce the highly toxic waste, no Democrat has offered an alternative for the spent fuel storage.

Auto standards

For Detroit, the Democratic proposals include both carrots and sticks. There is general agreement on the need for mandating increases in fuel economy standards for automobiles. Mrs. Clinton, for example, has called for an increase to an average of 55 miles per gallon by 2030; Mr. Edwards, 40 miles-per-gallon by 2016.

But, along with other Democrats including Mr. Obama, they have also proposed multi-billion dollar aid packages for the auto industry to help it research new technologies and retool factories to produce cleaner cars. The auto industry is also one of the prime beneficiaries of a fund Mrs. Clinton has proposed separately to help pay for the "legacy costs" of retiree health care benefits.

As they troll for votes in Iowa, the candidates form a united chorus of support for the use of ethanol.

Most of the candidates of both parties have also called for spending on research for clean-coal technology, including the capture and sequestration of carbon dioxide emissions. Mr. Edwards, for example, while the recipient of an enthusiastic endorsement of the United Mineworkers of America, has taken a hard line on new coal plants that do not capture greenhouse gases.

A UMW spokesman said the union's decision to back the ex-senator came in part because he has put forth what is, in the union's view, the most specific plans for research on coal's future.

Touting their foreign policy credentials, Gov. Bill Richardson of New Mexico and Sen. Joseph R. Biden Jr., D-Del., are among the Democrats calling for a renewed and more vigorous American role in international agreements to curb the release of greenhouse gases.

GOP cool on warming

Global warming in particular and energy in general have played a relatively less prominent role in the GOP nomination battle, a tendency reflected in the candidates' Web sites. While most of the Democratic candidates offer fairly detailed energy plans, the Republicans' debate, and their Web sites, have more abbreviated, broad-brush proposals.

In his standard stump speech, however, Mr. McCain regularly cites the "devastating" consequences of global warming and faults the Bush administration for being slow to respond to the issue. Some other Republican candidates, most notably former Sen. Fred D. Thompson of Tennessee, and U.S. Rep. Ron Paul, R-Texas, have been skeptical about the science behind assertions of global warming.

Others, such as former Gov. Mitt Romney of Massachusetts and former Gov. Mike Huckabee of Arkansas, are agnostic on the scientific debate, but support energy conservation and research for security reasons.

Mr. Huckabee pledges that his administration would achieve energy independence by the end of his second term. Mr. Romney offers a general everything-should-be-on-the table approach, endorsing research on a broad array of renewable energy, nuclear and fossil fuel sources. Former Mayor Rudolph W. Giuliani of New York has similarly called for an "Apollo project" to diversify the nation's energy sources, including nuclear, renewable sources and clean coal technologies.

In keeping with his libertarian philosophy, Mr. Paul opposes any significant energy role for the government, arguing that free markets will find a better path to the nation's energy future.