(Corrects quarterly period for Omnicom in last bullet point to Q3, not Q2)
PARIS, Oct 20 (Reuters) - Shares in France's Publicis GroupeSA fell on Thursday after underlying third-quartersales growth stalled, undershooting forecasts, and as thecompany's boss expressed caution over the prospects for nextyear.
Quarterly revenue rose by a mere 0.2 percent on an organicbasis to 2.32 billion euros ($2.55 billion), held back by thepreviously-flagged loss of large media accounts in the UnitedStates in 2015, but also missing the forecast by a Reuters pollof analysts that predicted growth of 0.97 percent.
Publicis Chief Executive Officer Maurice Levy said full-yearorganic growth in 2017 will be higher than in 2016, but pointedto the economic uncertainties following the British vote toleave the European Union, and surrounding the U.S. presidentialelection next month.
Shares were falling by 5.95 percent at 0808 GMT, on trackfor their worst day in four-and-a-half months, making Publicisthe worst-performer of the French CAC 40 stock index.
Publicis shares are up 2.7 percent since January.
* Nine-month revenue rose 1.9 percent on an organic basis to7.07 billion euros
* Publicis confirmed full-year guidance for 2016
* The advertising group, the world's third-largest, gainedclients such as Wal-Mart, P&G's home care products, Coty andUSAA.
* Management board will propose to bring forward the 2018target of a 42 percent payout to 2016.
* Levy said total acquisitions in 2017 should be lower than500 million euros.
* Levy, who is slated to leave his position as CEO in 2017,confirmed that the board would make a decision on his successorin February 2017.
* Levy said he was ready to take another position in thecompany's corporate governance to assure a smooth transition, ifthe board asked him to do so.
* American Rival Omnicom said this week that itsthird-quarter organic sales growth was 3.2 percent. UK-basedWPP, the top advertising company in the world, will reportthird-quarter sales on Oct. 31, while Havas will do the sameafter market close on Oct. 25. ($1 = 0.9116 euros) (Reporting by Mathieu Rosemain and Gwenaelle Barzic; editing byDiane Craft and Andrew Callus)