UPDATE 1-GDF agrees to sell SPE stake to EDF for $800 mln

(Adds details of sale, background)

PARIS, June 20 (Reuters) - Gaz de France GAZ.PA said on Friday it had agreed to sell its 25.5 percent stake in Belgian electricity company SPE to French power giant EDF EDF.PA for 515 million euros ($799.8 million).

Gaz de France said last month it had entered exclusive talks with EDF over the sale of its SPE stake, which the European Commission asked the French state-controlled group to divest as part of its plans to merge with Suez LYOE.PA.

The deal is subject to the successful conclusion of the Gaz de France-Suez merger, which is expected to be completed in the second half of July, Gaz de France said in a statement.

Its successful closure also depends on whether Britain's Centrica CNA.L, which also owns 25.5 percent of SPE, exercises its pre-emption rights to buy Gaz de France's stake or not. No mention of this was made in the statement.

Gaz de France said the price did not include “an additional purchase price due after commitments made by Suez Electrabel towards the Belgian state have been fulfilled.”

This additional amount is related to the right that would be granted to SPE to use some of the production capacity of nuclear plants operated by Suez’s Belgian subsidiary Electrabel.

This right had been negotiated by the Belgian state as part of the planned Suez-Gaz de France merger and was aimed at reinforcing SPE’s role as a competitor to Electrabel.

It is not yet known how much capacity SPE will be granted by Electrabel.

The Gaz de France-Suez merger has led to a shake-up of Belgium's energy sector. Last month, Suez agreed to sell its 57.5 percent stake in Distrigas DISTy.BR -- Belgium's main gas operator -- to Italy's ENI ENI.MI.

Reporting by Marie Maitre, editing by Richard Chang