* Bank prepares to move back-office jobs to Accenture
* Cost savings estimated at 90-160 mln euros
* 25 banks in being approached to join - source
By Lionel Laurent and Blandine Hénault
PARIS, Nov 22 (Reuters) - Societe Generale, France's No. 2 listed bank by value, is considering outsourcing 400 back-office jobs at its corporate and investment bank, according to internal memos seen by Reuters.
The plan, in which consulting company Accenture would take on staff working mainly in custody and securities services, could be extended to other businesses, such as broader financing, the memos drafted by management and unions showed.
"(It is) a project to transfer 400 jobs ... Accenture is asking that the transfer be mandatory," one memo drafted by the CGT union said, adding that cost savings had been estimated at 90-160 million euros ($115-205 million).
Investment banks across the world, including Switzerland's UBS and Royal Bank of Scotland, are cutting jobs and overhauling business models to adapt to tougher regulations and the economic slowdown.
"There is a competitive advantage in pooling together investments," said a memo drafted by SocGen management to present its new plan. "We need to be the drivers because if we don't act, our competitors will."
A SocGen spokesman said the bank was looking at a project with "an outside partner" to create a European back-office custody business that would offer services to rival banks.
He would not confirm the number of jobs affected, nor the possibility of expanding the remit of the plan.
The news was reported earlier by French investment newsletter L'Agefi.
If it goes ahead, the move will take effect in July, a union source told Reuters.
Another French bank is interested in taking part in the Accenture project, and 25 banks in total are being approached to join, the source added.
Five of the biggest staff unions at SocGen have called for a strike on Jan. 8 to protest against the threat of job cuts and salary freezes at the bank.
SocGen has spent the past year cutting costs and staff to slim down its balance sheet and replenish capital amid the grinding pain of the euro zone debt crisis.
It said on Nov. 8 that it had completed its plan to reshape its investment bank, but it warned that the outlook for 2013 remained murky.