* STOXX down 0.4 pct
* Key Trump adviser resigns
* German carmakers slip
* Advertisers dip as P&G reportedly trims budget
* France's ADP up on privatisation report (Adds shares, context)
LONDON, March 7 (Reuters) - European shares opened lower on Wednesday after the resignation of Donald Trump's economic adviser Gary Cohn, seen as a bulwark against protectionist forces within the U.S. government.
At 0857 GMT, the pan-European STOXX 600 index was down 0.4 percent while Wall Street futures were trading in negative territory.
"Gary Cohns departure rattled markets and equity markets look set to fall on the open. Stocks have declined overnight in Asia and its looking like it will be red today on the open", Neil Wilson, a Senior Market Analyst at ETX Capital told his clients in a morning note.
Most European markets and sectors were down, with Germany's DAX losing 0.5 percent.
German carmakers, which are expected to suffer from new U.S. tariffs, took a hit. Volkswagen lost 1.6 percent and Daimler 1.3 percent, the second and third worst performance of the German blue chip index.
Still in Germany, postal and logistics group Deutsche Post DHL was down 2.1 percent after reporting 2017 results.
Oil prices fell and London metals slipped, weighing on the energy and basic materials sectors, which were down 1.4 percent and 0.8 percent respectively.
The advertising sector retreated after the Financial Times said P&G would cut agency spending by 1.25 billion dollars over three years. France's Publicis and Britain's WPP fell 1.9 percent and 1.6 percent respectively.
British plane engine maker Rolls-Royce was the best Stoxx index performer, surging 8.5 percent after saying it remained on track to meet its financial goals for 2020.
Second came Smurfit Kappa, after U.S. peer International Paper revealed the takeover offer it made for Europe's largest paper packaging producer was worth 8 billion euros.
Shares in ADP came in third, up 2.3 percent, after a media report said the government would go ahead with plans to privatise French airport operator ADP and sell its 50.6 percent stake entirely.
French construction group Vinci, which has an 8 percent stake in ADP and expressed an interest for acquiring more, rose 0.4 percent. (Reporting by Julien Ponthus Editing by Tom Pfeiffer and Raissa Kasolowsky)