Britain's PM backs fracking for shale gas

* Fracking could cut bills, create jobs - Cameron

* Risks angering rural supporters, environmentalists

* Protests have hit ruling party heartland

LONDON, Aug 12 (Reuters) - Britain's Prime Minister DavidCameron has given his unequivocal backing to the divisive"fracking" process used to extract shale gas from rocks, riskingangering his party's supporters from more rural areas.

Britain is thought to have major shale gas reserves whichcould help reverse a rising dependency on energy imports, butthe energy industry is having to tread carefully to reassure asceptical public and vocal environmental lobby.

Fracking for shale gas could help reduce energy bills,create jobs and provide extra funds for communities where theresource is found, Cameron wrote in an editorial in Britain'sDaily Telegraph newspaper on Monday.

"If we don't back this technology, we will miss a massiveopportunity to help families with their bills and make ourcountry more competitive," the leader of the governingConservative Party wrote.

Hydraulic fracturing or fracking retrieves gas and oiltrapped in tight layered rock formations by injectinghigh-pressure water, sand and chemicals.

Critics say it can trigger small earthquakes, pollute thewater supply and spoil pristine parts of the countryside.

Protesters have been active at one drilling site inBalcombe, West Sussex, in a constituency in the Conservativeparty's traditional southern heartland.

Cameron said he supported fracking in both the north andsouth of the country, dismissing recent suggestions by alawmaker that the process could be confined to less populous andremote areas in the north.

Cameron argued fracking was safe and, if it was properlyregulated, there was no evidence it would contaminate watersupplies or cause environmental damage.

Centrica