Hydraulic fracturing, the controversial drilling technique also known as fracking, has lifted U.S. energy output dramatically, despite warnings from critics who fear it pollutes water deep underground.

Any shift in public opinion could impact policy - and huge sums in energy spending - since drilling regulations are under review by the Obama administration and local officials around the country. The high stakes involve a range of issues from U.S. energy independence, to protection of drinking water.

Both sides are using movies to try to win the debate, though actor Matt Damon says viewers should not assume the movie he stars in, "Promised Land," is "a rabid anti-fracking polemic."

In the film, Damon plays a gas company landman - an agent who buys or leases land - intent on drilling beneath a town where some residents are concerned about the perils of fracking. As the landman gets to know the townspeople, he suffers a crisis of conscience.

In an interview in Los Angeles, Damon said he worries that viewers will wrongly assume the film is one-sided and not see it. He declined to offer his personal view on fracking. "That's not the point. The point is that (the film) should start a conversation."

The Northern Irish director Phelim McAleer's documentary, "FrackNation," is an unabashedly pro-drilling mantra set to air next month on AXS TV, the cable network controlled by Dallas Mavericks owner and media mogul Mark Cuban.

McAleer views fracking as "the best thing ever," a potential savior for the U.S. economy, unless the forces he likes to call "Big Enviro" succeed in derailing it.

On the other side of the argument, HBO, the cable pay channel, could air a sequel to "Gasland," a scathing 2010 documentary from director Josh Fox, as early as next year.

The original film featured scenes of tap water erupting into flames and mobilized environmental groups against fracking, drawing full-throated rebuttals from an oil industry that says the process has never caused water problems.

Fox declined comment for this article.

Amid the showdown, both industry and anti-fracking camps have mounted major campaigns to sway hearts and minds.

"It could become the biggest environmental debate of our time," said Robert McNally, an energy policy expert and former White House adviser under George W. Bush. "Hollywood is taking notice, and the industry will have its work cut out for it to defend fracking."

Nearly four out of ten Americans surveyed by the Pew Research Center early this year said they knew nothing about fracking. Other polls show most Americans familiar with the practice believe fracking offers economic benefits but requires tougher regulation.

This year, for the first time, U.S. online searches for the term "fracking" became more popular than "climate change," Google data showed. Fracking has doubled on Google's popularity index since last year, and while "global warming" still draws more hits, the gap is narrowing.

Drinking water contamination is the leading environmental concern among Americans, according to Gallup polling data. A Bloomberg National Poll this month showed that 66 percent of Americans want more fracking regulation, up from 56 percent in September.

'POUNDING THE ZONE'

Whether "Promised Land" will shift public opinion is uncertain. But films with environmental themes often can, according to Joseph Cappella, a professor of communications at the University of Pennsylvania.

Past examples include Al Gore's "An Inconvenient Truth" on climate change, and "Erin Brockovich," a dramatization of real events in which actress Julia Roberts played a legal clerk who uncovers water contamination by a California power company.

Ahead of the release of "Promised Land," some within the oil industry are already reading the film's script online.

"Look, I don't want to whistle past the graveyard. This film is going to be a challenge, and we'll just have to see how it does on opening weekend," said Chris Tucker of pro-drilling group Energy In Depth (EID), which is funded by industry. "In terms of popularization of the issue, it will have an effect."

The oil industry wants to avoid another blow like the one it took from Fox's 2010 "Gasland" film. Google search data shows online interest in fracking surged immediately afterwards.

For three years, Tucker has been working with other communications experts, "pounding the zone with facts" to counter what he calls false claims in "Gasland" and to promote drilling.

Films like "Promised Land" will get people curious and send them searching online, said Tucker, where he worries the term 'fracking' gets a bad rap. "People will go home and Google it, and the other side does really well on Google," he said.

EID released its own pro-drilling film, "Truthland," this year, dubbing it "the factual alternative to Gasland."

LOSING PR BATTLE?

In some ways, the film blitz may be behind the times. Fracking has already come to dominate U.S. drilling over the last half-decade: Onshore rigs doing so-called unconventional drilling account for nearly two-thirds of the total.

Tucker and industry officials are regulars at conferences, in newspaper op-ed articles, and on TV to defend drilling.

On the environmentalist side, Fox travels widely to lead anti-fracking rallies, sometimes rousing crowds by playing a banjo, which is also featured in the Gasland soundtrack. He has enlisted help from artists including Yoko Ono and Sean Lennon.

"The lesson of 'Gasland' is that public perception is a very big part of the equation," said Jonathan Wood, a political risk analyst at London-based Control Risks, whose clients include oil companies.

In a report this month, Wood wrote that the industry has "largely failed to appreciate social and political risks, and has repeatedly been caught off guard by the sophistication, speed and influence of anti-fracking activists."

Hydraulic fracturing entails pumping water laced with chemicals and sand at high pressure into shale rock formations to break them up and unleash hydrocarbons.

The minerals are trapped thousands of feet below water tables, but critics worry that fracking fluids or hydrocarbons can still leak into water tables from wells, or above ground. Among their other concerns: fracking-related earthquakes, and growing dependence on fossil fuels.

The United States now rivals Russia as the world's top gas producer, in large part due to fracking, and has stemmed a long decline in oil output, which stands at an 18-year high near 7 million barrels a day.

So far, the Obama administration has cautiously endorsed the new drilling, but the U.S. Department of Interior is working on new fracking rules on public lands starting next year.

Some drillers have faced fracking-related fines for water contamination due to spilled fracking fluid. Last year, after sampling water in rural Pavillion, Wyoming, the Environmental Protection Agency (EPA) presented the first-ever U.S. government finding of a potential link between fracking and water contamination.

More broadly, however, the EPA condones fracking on safety grounds. But unlike the growing consensus among climate scientists linking global warming and industrial activity, there is no consensus that fracking poses a danger. Unconventional drilling has surged only over the last half decade.

The EPA will release an in-depth study on fracking's potential impacts on water supplies in 2014.

Tough economic times can widen support for drilling. A national Gallup poll this year showed that more Americans favored prioritizing economic growth over the protection of the environment (49 percent versus 41 percent).

That's a reversal from 2007, when 55 percent favored environmental protection.

Cuban is betting the hot potato issue will draw viewers to "FrackNation" on his cable channel.

"Op-Ed-umentaries like this are supposed to make people think about the topic, which is always a good thing," he said.

(Reporting By Joshua Schneyer and Edward McAllister in New York; Additional reporting by Zorianna Kit in Los Angeles; Editing by Jeffrey Benkoe)

• A Permanent Economic Emergency