UPDATE 3-Carrefour in talks to buy main French franchisee

* Discussions under way but no certainty a deal can be reached

* Carrefour may sell stake in Altis to fund part of deal-source

* Carrefour declines to comment

* Guyenne shares up 4.1 percent, Carrefour shares off 1.2 pct (Adds source comment on Altis, analysts, updates shares)

By Dominique Vidalon

PARIS, Dec 8 (Reuters) - Carrefour is in talks to buy its largest franchisee in France, Guyenne et Gascogne, as a key shareholder in the franchisee looks to sell out and the world's No.2 retailer seeks to shore up its position in its home market.

The two sides confirmed in separate statements on Thursday that discussions were under way but said it was not certain a deal would be reached.

The talks were touched off by the end of a lock-up that had barred Guyenne et Gascogne's main shareholder, the Beau family, from selling before Dec. 15.

"Carrefour seems forced to do this deal with the Beau family at a decent price, although it doesn't create any synergies for the group," said one analyst on condition of anonymity, adding Carrefour could be in a "lose-lose" situation of either overpaying or losing the franchisee to a rival.

"The timing is of course awful for Carrefour which already has a lot of troubles in running the group as it is now," he added, referring to a string of profit warnings from the group this year, mainly due to problems in France.

Guyenne et Gascogne said, however, that any agreed deal would exclude the impact on its shares from press reports this week about a potential Carrefour takeover.

Guyenne at Gascogne shares closed at around 80 euros last week, valuing the business at about 500 million euros ($670 million). At 1335 GMT, the stock was up 4.1 percent at 88.55 euros, while Carrefour's was down 1.2 percent at 18.23 euros.

LIMITED FINANCIAL LEEWAY

Le Figaro newspaper said on Wednesday Carrefour was likely to pay for any deal in shares given its limited financial leeway.

Analysts said an all-share deal may be difficult to engineer after Carrefour's shares plunged 40 percent this year following repeated profit warnings and strategy U-turns.

An industry source told Reuters on Thursday that Carrefour could also sell its stake in franchisee Altis, a joint-venture between Carrefour and Spanish retailer Eroski, to fund part of the deal, confirming a report by French daily Les Echos. Carrefour declined to comment.

Taking over Guyenne et Gascogne, which operates stores primarily in southwest France and Spain, would allow Carrefour to keep more revenue from its French operations and fully consolidate Spain, according to analysts.

Carrefour earns some 40 percent of its revenue in France, where it has faced tough competition from Leclerc, Casino and Auchan supermarkets.

Founded in 1913, Guyenne et Gascogne had consolidated net sales of 533 million euros last year.

On Wednesday, Guyenne et Gascogne Chairman Bertrand de Montesquiou had told Reuters his group was in talks with Carrefour that included expanding equity ties and that it might receive a proposal soon.

Carrefour and Guyenne et Gascone have a relationship dating back over 40 years, which they renewed in 2008.

Together they own Sogara, which they set up in 1966 and which operates 13 Carrefour hypermarkets in south west France. Sogara in turn owns 8.2 pct of Centros Commerciales Carrefour, which operates 171 Carrefour hypermarkets, 108 Carrefour Market supermarkets and 28 Carrefour Express stores in Spain.

Guyenne et Gascogne itself also operates 6 Carrefour hypermarkets and 27 Carrefour Market supermarkets in France. ($1 = 0.7468 euros) (Reporting By Christian Plumb and Dominique Vidalon, additional reporting Pascale Denis; Editing by David Cowell and Mark Potter)