UPDATE 2-JCDecaux yet to see sustained ad market upturn

* Q3 sales 431.8 mln euros

* Q3 underlying sales down 12.1 pct

* Ad mkt bottomed in Summer, no signs of sustained recovery

* Expects 2009 operating margin slightly ahead of that of H1

(Adds share reaction, analyst comments, details)

By Dominique Vidalon

PARIS, Nov 4 (Reuters) - JCDecaux (JCDX.PA) on Wednesday said revenue and profitability would fall this year and it had yet to see sustained signs of a recovery, although the worst might be over for the battered advertising sector.

The world's No. 2 outdoor advertising group, behind Clear Channel Outdoor (CCU.N), made the forecast after closely-watched underlying sales fell 12.1 percent in the third quarter to 431.8 million euros ($631.7 million), ahead of company's guidance.

"We believe that the advertising market bottomed out in the Summer and while some further improvement is anticipated in the fourth quarter, in part due to comparables, we are not yet seeing sustained signs of an advertising recovery and business continues to be volatile," co-Chief Executive Jean-Francois Decaux said in a statement.