** Barclays says it has been a long-standing agency bull but came away from Cannes ad festival meetings more bearish than before

** While the brokerage still believes that "agencies will adapt, survive and ultimately thrive" in an AI world, they need time, money, and execution to adapt, it says

** Barclays downgrades US advertisers Interpublic IPG.N and Omnicom OMC.N to "equal-weight" from "overweight," citing anticipated challenge from artificial intelligence

** Broker also downgrades British advertising and public relations firm WPP WPP.L, expecting continued underperformance amid AI turn

** The brokerage maintains France's Publicis PUBP.PA at "overweight," citing their strong position to navigate AI buildup

** It also keeps its bullish stance on Havas HAVAS.AS, rating the stock "overweight" as in its view it warrants a 15% discount to peers

(Reporting by Leo Marchandon)

((Leo.marchandon@thomsonreuters.com))