UPDATE 2-EDF seeks 20 pct tariff hike; bond raised $4.5 bln

* Says needs 20 pct French power tariff hike over 3 years

* Says to cut investments if government refuses tariff rise

* Says raised 3.2 bln euros in retail bond offering

(Updates with La Tribune interview)

PARIS, July 8 (Reuters) - France's EDF (EDF.PA) will ask the government for permission to raise electricity tariffs by a fifth over the next three years to help it reduce debt, Chief Executive Pierre Gadonneix told two French publications.

"In order for us to stop getting into debt, we would need a 20 percent rise in tariffs. This could be spread out over three years, for example, or for a bit longer," Gadonneix told French magazine Paris Match and daily newspaper La Tribune in separate interviews that were due to be published on Thursday.

"An adjustment is necessary," he told La Tribune, adding that French power tariffs would be 40 percent higher than they currently are if the state-owned group had been able to pass on the cost of inflation into its prices over the past 25 years.

French power and gas tariffs are set by the government.

If the government refused a 20-percent increase, Gadonneix told Paris Match that EDF, which is more than 80 percent owned by the French state, would have to slash investments.

EDF has plans to invest 7.5 billion euros in France in 2009 alone. On Monday, it closed an offer for a retail bond, which reportedly raised nearly 3 billion euros, and the group has been active in the debt market in recent weeks.

The group's debt stood at 24.5 billion euros at the end of 2008, up from 16.3 billion euros a year earlier following the acquisition of British Energy.

"The sums are simple. For example, an EPR (European Pressurized Reactor) costs 4 billion euros whereas if we prolong the life span of our reactors from 40 years to 60 years, the cost is 400 million euros per plant. This is therefore the most profitable investment for the French population," Gadonneix said.

The French nuclear safety authority ASN said on Tuesday it had agreed in principle for EDF to continue running its oldest nuclear reactors for up to 40 years. EDF wants the life span of its reactors to go up to 60 years, arguing that this had been granted for similar reactors in the United States. [ID:nL7660353]

Asked by Paris Match whether the EPR was not a priority for EDF, Gadonneix said: "The priority is to prolong the life span of our reactors, while ensuring that future generations benefit from the EPR technology.

"This is the reason why EDF supports and finances this technology in the countries where nuclear will develop, such as in China, the UK and the United States."

Gadonneix also told La Tribune that EDF had raised around 3.2 billion euros ($4.45 billion) in a retail bond offer aimed at financing a 7-billion euro investment plan in France.