(adds broker comment, updates prices) BEIJING, March 21 (Reuters) - Shanghai copper prices fell for a fourth day on Wednesday, touching their lowest in almost six months amid fears of a trade war as investors waited for news on a U.S. interest rate hike. Short positions on the most traded May copper contract on the Shanghai Futures Exchange (ShFE) have risen above 100,000 lots this week and exceed long positions by more than 16,000 lots, ShFE data show. Markets are waiting to take their cue from the Federal Reserve's decision on interest rates later in the day, Malcolm Freeman, CEO of Kingdom Futures, wrote in a note. Higher U.S. rates may support a rising dollar, which would limit demand for dollar-denominated commodities such as copper from buyers paying with other currencies. "Aside from this there is also the growing paranoia around the possibility of a global trade war which appears in balance to be frightening the more speculative investors away from the sector," Freeman added.
* SHFE COPPER: The May contract was down 1 percent at 50,840 yuan ($8,030) a tonne by the mid-session interval. It earlier touched 50,640 yuan, its lowest since Sept. 25.
* LME COPPER: Three-month copper on the London Metal Exchange was up 0.2 percent to $6,769 a tonne by 0518 GMT, gaining some respite from a weaker dollar after touching $6,730 a tonne on Tuesday, its lowest since Dec. 14. Trading volumes reached only 857 lots as traders waited on the Fed.
* INVENTORIES: LME copper stocks <MCUSTX-TOTAL> grew by a further 3,200 tonnes on Tuesday to 322,475 tonnes, bringing this month's rise to 61 percent.
* COPPER: Workers at Antofagasta PLC's Los Pelambres copper mine in Chile have opted to extend a period of government mediation in an effort to reach agreement on a new labor contract, an industry group said on Tuesday.
* ALUMINIUM: Global primary aluminum output excluding China dipped to 2.009 million tonnes in February from a revised 2.221 million tonnes in January, International Aluminium Institute (IAI) data showed on Tuesday.
* TARIFFS: The United Arab Emirates is asking Washington to exempt it from new U.S. tariffs on aluminum and steel and believes it has a strong case, a senior government official said on Tuesday. For the top stories in metals and other news, click or
* A hush settled over financial markets on Wednesday as investors waited to hear how often the Federal Reserve might hike U.S. rates this year, while the currencies of exporting nations were rattled by fears of a full-blown trade war.
Three month LME copper 6769 Most active ShFE copper 50840 Three month LME aluminum 2082 Most active ShFE aluminum 13890 Three month LME zinc 3206 Most active ShFE zinc 24430 Three month LME lead 2365 Most active ShFE lead 18330 Three month LME nickel 13440 Most active ShFE nickel 101480 Three month LME tin 20760 Most active ShFE tin 144010 LME/SHFE COPPER LMESHFCUc3 903.5 LME/SHFE ALUMINIUM LMESHFALc3 -1422.86 LME/SHFE ZINC LMESHFZNc3 391.61 LME/SHFE LEAD LMESHFPBc3 118.95 LME/SHFE NICKEL LMESHFNIc3 852.31
($1 = 6.3312 Chinese yuan renminbi)
(Reporting by Tom Daly; editing by Richard Pullin)