“DRILL, baby, drill.” It is among the best-remembered lines of the 2008 presidential campaign, colorfully capturing the desire of many Americans for cheap, reliable energy produced at home rather than in unpredictable places like Iran or Venezuela.       

No slogan in the current presidential campaign has emerged to match it, but energy has taken center stage again as an issue that encompasses concerns about the environment and national security, and now, even more pressingly, economic revival.       

Presidential campaigns have a way of producing stark contrasts between candidates. In the presidential debates, President Obama and Mitt Romney clashed sharply on fossil fuels and renewable energy.       

The Republican nominee accused the president of picking a lot of losers with $90 billion worth of government largess for Solyndra, the California solar company, and other green enterprises. “And by the way, I like coal,” he said in the first debate. Mr. Obama countered that the oil industry was the true recipient of “corporate welfare” in tax breaks: “Does anybody think Exxon Mobil needs some extra money, when they’re making money every time you go to the pump?”       

But such differences may be more rhetorical than real; the marketplace, technological change and Middle East tensions are driving Mr. Obama and Mr. Romney to much the same place on the country’s energy future.       

Both candidates say they support nuclear power and biofuels, though neither is advocating strongly for either. Both say they want to encourage more oil drilling in places like North Dakota, Texas and Alaska to lower dependence on oil from the Middle East. Even while the current administration’s Environmental Protection Agency has more aggressively regulated mining and drilling, Mr. Obama, like Mr. Romney, has celebrated the boom in domestic natural gas production and wants to spread its use for power production and even export.       

In a twist few would have predicted when Mr. Obama first entered the White House and much as it may dismay him, fossil fuels have eclipsed renewable energy and climate change in the national discussion — even as climate scientists warn that the droughts that scorch corn crops and the faster melting of Arctic ice and glaciers around the world are signs of things to come.       

“Last time we were electing a president, it looked like we were running out of energy, and this time we’re debating how to use what now seems to be ample resources for decades to come,” said Daniel Yergin, the energy historian. “The country needs to decide the pace and scale of domestic energy development as well as the mix among oil, natural gas, coal, renewable and nuclear we will use. But the marketplace itself will have a bigger role than the election campaign in what the mix eventually will be.”       

The oil and shale gas drilling boom is reshaping the nation’s energy map, and it is still difficult to predict the extent of its ramifications. With domestic oil production climbing rapidly since 2008, oil imports have been cut to just over 40 percent of domestic supplies, the lowest level in two decades, from 60 percent.       

Over the same period, domestic natural gas production has risen by 15 percent, producing a glut that has forced down the gas price by nearly two-thirds. Plentiful, cheap natural gas has crowded out much of the expected growth of renewable energy like wind and solar power, but it has cut domestic consumption of dirtier coal even more sharply.       

Electrical generation from wind, solar, geothermal and biomass have expanded to 5.8 percent of the country’s electricity, from 3.1 percent, since Mr. Obama took office, partly because of tax incentives and other support from the administration’s stimulus package. But the expansion of power driven by natural gas has arguably been even more impressive. Cheap natural gas fuels a bit more than 30 percent of American power production, up from just over 20 percent in 2008.       

On the stump, Mr. Obama has not been shy in heralding the boom in domestic oil and gas drilling under his watch. Not to be outdone, Mr. Romney has put “energy independence” — including the expansion of hydrocarbon exploration and production, building the Keystone XL pipeline from Canada and removing federal regulations on coal — at the top of his five-point plan to produce millions of jobs.       

Certainly the two have different energy visions. Mr. Romney’s proposal to expand state regulatory control over drilling and mining on federal lands would represent a break from government policies dating back to Theodore Roosevelt, in the highly unlikely event that Congress could be coaxed to go along. And the two candidates are on opposite sides of a gaping divide over coal, with Mr. Obama pushing to phase out coal-fired electrical generation while Mr. Romney favors burning more coal to keep mine operations rolling.       

But how much does the nation’s energy future depend on who wins the race?       

No doubt the nation has several important decisions to make in the next couple of years. Should it limit hydraulic fracturing, the contentious method of blasting water through tight rocks to gain access to oil and gas, with new regulations? Should the federal government aggressively open up more offshore drilling in Alaska’s Arctic and off the coasts of Virginia and the Carolinas? Should it export vast amounts of its new bounty of natural gas, potentially jeopardizing the low price that is currently benefiting domestic consumers and manufacturers? Should the country allow construction of the Keystone XL pipeline, which would secure oil supplies from Canada, but also guarantee the spread of mining for oil sands, which has a higher carbon footprint than most conventional oils? Does coal, the dirtiest fossil fuel, have a future in America?       

Either Mr. Obama or Mr. Romney will have to decide along with, of course, the new Congress and in many cases the states. The two candidates and their parties have different constituencies that are tugging them in opposite directions on these questions. But the election will probably matter only on the margins of energy policy. The same cannot necessarily be said, however, about the flip side of energy policy — environmental policy — where a Romney Environmental Protection Administration would probably look very different from Mr. Obama’s.       

“I think on oil and gas production, pipelines and natural gas exports the differences between the two are marginal,” said David Goldwyn, formerly the State Department’s coordinator for international energy affairs under Mr. Obama, “but on greenhouse gas emissions issues the differences are significant.”       

Mr. Romney has proposed excluding greenhouse gases from the Clean Air Act, reversing new mercury standards for coal and slowing the advent of automobile fuel efficiency standards, and he could be expected to use his executive and regulatory powers to make policy adjustments. Nevertheless, he would probably need support from Congress and the courts to veer radically off the established Obama course.       

With the economy still weak and the federal government in financial crisis, new energy tax incentives, mandates and subsidies are pretty much off the table, no matter who is elected in November. Politicians of both parties have learned from the Solyndra fiasco about the risks, financial and political, of spending taxpayer money on solar and other renewables, given their continuing problems competing in the marketplace. Even the wind production tax credit, so crucial to the expansion of wind farms around the country, is about to expire, and wind power companies are letting workers go. Apparently Mr. Obama is not able to save the tax credit from Congressional budget-cutters, and as president, Mr. Romney would not want to save it.       

Both a second Obama administration or a Romney administration would most likely support new exports of liquefied natural gas, given the domestic bounty and opportunity to reduce the trade deficit, although Democratic and Republican energy experts have suggested that regulatory approvals for proposed export terminals are not likely to happen quickly, to leave time to measure the impact exports might have on domestic gas prices.       

The Obama administration opposed approval of the Keystone pipeline last January mainly because of Nebraska’s concerns about its route over a sensitive aquifer. Now that Keystone has altered the route, many energy experts, including some Democrats, expect Mr. Obama to go along, to create jobs but also to replace oil shipments from the Persian Gulf and Venezuela.       

To the dismay of environmentalists, the Obama administration is still pushing for oil drilling in the Alaskan Arctic, though the president seems less likely to approve drilling off the Carolina and Virginia coasts, where many experts doubt that there are large reserves to be found anyway.       

It is true that Mr. Obama still talks up developing renewable energy sources and his concern over climate change, but the campaign rhetoric has clearly shifted from four years ago, when he and his Republican opponent at the time, Senator John McCain of Arizona, favored some form of carbon cap and trade legislation to combat global warming. Not even the Democrats mention reviving market-based emissions trading anymore, after that stalled in Congress nearly three years ago.       

Instead, Mr. Obama, who originally ran as a champion of solar and wind power, has presided over the nation’s greatest fossil fuel boom since the discovery of Alaska’s giant Prudhoe Bay field more than four decades ago. After temporarily halting oil and gas drilling in the Gulf of Mexico after the disastrous 2010 BP spill, he reopened the gulf for drilling and then expanded offshore exploration to the Alaskan Arctic for the first time in decades. In their party platform at their convention this summer, Democrats advocated even greater production of domestic natural gas. The Obama administration established some new emissions standards for hydraulically fractured wells, but gave the oil and gas industry plenty of time to comply and otherwise tilted in their favor, and there is no sign a second Obama administration would be tougher. With the exception of New York State and a few other localities, little has been done through governmental authority to slow the boom in hydraulic fracturing.       

Energy politics have shifted because a persistently sluggish economy with roughly 8 percent of American workers unemployed has made it a pocketbook issue. The oil and gas boom has produced one of the economy’s few bright spots. Drilling and support jobs have increased by nearly 25 percent since the first half of 2008 to nearly 200,000 jobs, despite the financial collapse and recession. Those jobs pay about $34.50 an hour, nearly 50 percent higher than the national average. A refinery boom based on new domestic oil and gas production has made the United States a refined petroleum product net exporter for the first time since the Truman administration.       

Several petrochemical plants are being planned or expanded on the coast of the Gulf of Mexico, steel plants in the Midwest are adding shifts to build oil and gas pipelines, and many economists predict a manufacturing renaissance based on low prices of natural gas — a key component for the manufacture of plastics, fertilizers and chemicals. To save on costs, municipal governments and companies are switching thousands of buses and trucks every year from diesel to natural gas fueling.       

“Both candidates are trying to stay out of the way of the gas boom,” said William K. Reilly, who was administrator of the E.P.A. under the elder President Bush. “It’s associated with thousands of jobs that are on everybody’s mind right now. And beyond that, it’s raising the possibility of a new industrial renaissance.”       

According to the Dow Chemical Company, cheap domestic natural gas has allowed the industrial sector to add 500,000 jobs since 2010. The company has also assembled a list of 91 proposed plant investments announced by Dow and many other companies over the last 18 months because of the lower gas prices; they are valued at $70 billion and represent one to three million jobs for the production of steel, aluminum, tires, machinery and other products, Dow says.       

The biggest difference between the candidates is over coal, but even there the ultimate policy differences may be a lot narrower than environmentalists or coal companies would want or expect. A Romney television commercial blanketing the airwaves in coal-producing states captures the urgency of the issue with a miner accusing the Obama administration of “attacking my livelihood.”       

Mr. Obama has worked to shut down older coal-fired power plants. He has pushed policies regulating mercury, hazardous air pollutants like sulfur dioxide and greenhouse gases. But concerns about lost coal mining jobs have slowed other environmental initiatives to control ozone emissions and coal ash, and few energy experts say they think a second Obama administration would apply many new regulatory controls until the economy picked up. Mr. Romney has pledged to repeal the Obama coal regulations, although that would require Congressional approval, which would be very difficult without a big Republican majority in the Senate. Even then, some regulatory reversals could be challenged in the courts. And finally, many states have adopted their own tough anti-coal regulations.       

A Romney administration would most likely try to help the coal-mining companies by discontinuing the characterization of carbon dioxide as a pollutant under the Clean Air Act, which gave the E.P.A. powerful new authority to control greenhouse gases. Since the courts upheld the authority, it would take an amendment to the Clean Air Act to exclude the gas. That would require 60 votes in the Senate, which would be extremely difficult.       

Whatever the Romney administration might try, coal appears to be on a steep downward slide. About a third of the nearly 600 coal plants in the United States are over 50 years old, and most energy experts say they believe all of those will be out of service over the next 20 years or so. While a few new coal plants may be built, for the most part the older plants will be replaced by gas-fueled plants, many of which can produce electricity for less than half of what it costs to run a coal-fired unit because of the gas glut and price collapse.       

“Coal will regain a bit of market share as natural gas prices recover somewhat, but most coal-to-gas substitution will be permanent,” according to a recent Moody’s Investors Service report, which predicted that over the next decade, coal’s share of domestic electricity mix would drop to a third from a current 40 percent. (Coal represented 48 percent of the mix in 2008.)       

A Romney administration would probably try to encourage more coal exports to compensate for lower domestic demand. The coal industry is angling to build several export facilities in Washington and Oregon. But the proposed ports face a lengthy permitting process, and the two environmentally sensitive states remain responsible for resolving many of the issues no matter who is president.       

“The future of coal as a fuel of choice for power plant operators appears to be on an irreversible decline regardless of who is elected, though who is elected will effect the rate of decline,” said Michael Webber, associate director of the Center for International Energy and Environment Policy at the University of Texas at Austin. “Obama would speed it up and Romney would slow it down, but it will happen regardless. Even the president, as powerful as he is, cannot overcome the fundamentals of the market, and the market says coal’s days are numbered and the market sees gas as the rising star.”