* Shell Q3 profit falls 15%, shares down
* China doubts long-term trade deal with Trump
* STOXX 600 logs second straight monthly gain (Updates to close, adds comments)
By Shreyashi Sanyal and Agamoni Ghosh
Oct 31 (Reuters) - European shares fell on Thursday, hurt by losses for miners and automakers as doubts grew over the prospect of a trade deal between the United States and China, with weak earnings from oil major Royal Dutch Shell adding to the gloom.
A Bloomberg report said that China is doubtful of a long-term trade deal with U.S. President Donald Trump, raising fresh uncertainty about progress between the two countries after an interim trade deal was almost finalised.
The report dashed optimism earlier in the session sparked by the U.S. Federal Reserve lowering borrowing costs for the third time this year on Wednesday.
The pan-European STOXX 600 index ended 0.5% lower but logged its second straight monthly gain after an October packed with corporate earnings reports along with some Brexit and trade twists.
"The pain inflicted by the trade war on the U.S. economy may eventually make it more willing to compromise but the question is how much pain is needed for a full deal to be signed," said Timme Spakman, economist, international trade analysis at ING.
Tariff-exposed miners were down 1.4%, while automakers lost 1.3%.
However, the biggest decliners were oil and gas producers , which fell 1.7% after heavyweight Royal Dutch Shell slid 4%.
Shell warned uncertain economic conditions could slow its $25 billion share buyback plan. That followed warnings from BP and France's Total earlier this week about lower oil and gas prices hitting margins.
Airlines also posted some disappointing numbers.
Air France-KLM fell 1% after it said slowing travel demand was likely to hurt ticket sales in the remainder of the year, while British Airways owner IAG said industrial action by pilots at the airline had knocked third-quarter profits.
In the auto sector, a deal between Fiat Chrysler and Peugeot owner PSA to create the world's fourth-largest automaker lifted the shares of Fiat Chrysler 8.2%.
However, PSA fell about 13%, after having risen nearly 5% in the last three sessions in the run-up to the deal.
Spanish utility Enagas jumped 5.5% after a media report said a Spanish regulator was considering softening proposed cuts to gas grid returns. (Reporting by Shreyashi Sanyal in Bengaluru; Additional reporting by Agamoni Ghosh; editing by Patrick Graham, Arun Koyyur, Kirsten Donovan)