* Many energy experts say reactor is unnecessary
* Sarkozy says Penly key to export French nuclear know-how
* Socialists say will shut 24 out of 59 reactors by 2025 if elected (Adds reaction from green groups)
By Muriel Boselli
PARIS, Nov 25 (Reuters) - France will go ahead with a controversial project to build a 60th next-generation nuclear reactor, President Nicolas Sarkozy said on Friday, as he stepped into a heated pre-election debate over France's dependence on atomic power.
During a visit to Pierrelatte near the Tricastin nuclear power plant in southern France, the French president said the pre-electoral pact by the Socialists and Greens parties to shut 24 reactors across France by 2025 was a threat to the country's industry and the purchasing power of French households.
He reiterated his right-leaning ruling UMP party's will to power ahead with its nuclear programme and said the proposal to shut down more than a third of the country's reactors would cost French consumers 5 billion euros ($6.63 billion) a year.
While the Fukushima catastrophe in Japan in March has fuelled speculation France would give up its plans to build the Penly reactor, in northwestern France, the government has repeatedly denied the project has been ditched.
"We maintain the project to build a reactor in Penly," Sarkozy, who has yet to make his candidacy official for the 2012 presidential election, said on Friday.
"Launching new projects in France is an essential condition to sell our know-how abroad," he said.
Sarkozy first announced the project in 2009 but many energy experts have said the reactor is unnecessary as France, which already operates 58 reactors, needs electricity plants which can be turned on and off easily to respond to peak demand.
A 59th reactor is currently under construction in Flamanville in northwestern France, and the project is hit by delays and cost overruns.
"Someone will have to explain to me how we will tell the Indians and Chinese to buy French reactors after having shut 24 reactors (at home)," Sarkozy said.
With presidential elections looming in April 2012 and legislative polls shortly afterwards, the Socialist Party and the Greens struck a deal last week on positions covering a range of policies, including the divisive issue of nuclear energy.
Both parties agreed to shut France's 24 oldest reactors by 2025 and build no new reactor, marking a U-turn in socialist ideology.
Socialist president Francois Mitterrand deployed the French nuclear energy programme in the 1980s and early 1990s to boost France's energy independence.
"The swirl of ever more exaggerated numbers makes your head spin," the green campaign group Greenpeace said on Friday in reaction to Sarkozy's comments, adding numbers recently quoted for nuclear-related job losses ranged from 200,000 to 2 million.
"The president and the UMP are pretending to forget the huge number of jobs which would be created by the dismantling of reactors in France and abroad, managing nuclear energy waste and through the development of renewables," it said in a statement.
State-owned nuclear power producer EDF recently delayed by a few months public consultations necessary to give the go-ahead for construction of Penly, blaming safety tests carried out after the Fukushima disaster.
Penly, which would be France's second new-generation reactor after the one being built in Flamanville, was originally due for construction from 2012 and set to start production from 2017. ($1 = 0.7536 euros) (Additional reporting by Marie Maitre; editing by Jason Neely and James Jukwey)