* Some investors taking profits - ABN AMRO
* Copper poised to finish 3.1 pct down on the week
* Inventories register biggest weekly inflow since May
* LME/ShFE arb: http://bit.ly/2wZSAEz (Updates prices)
LONDON, Sept 15 (Reuters) - Copper prices on Friday were set for their biggest weekly fall since December as investors took profits from a speculative rally to three-year highs and data showed that U.S. industrial output fell in August.
Some investors were taking profits but supply deficits and solid demand for metals in top consumer China would likely keep prices around current levels through this year, said ABN AMRO analyst Casper Burgering.
COPPER: Benchmark copper on the London Metal Exchange was down 0.3 percent at $6,481 a tonne by 1355 GMT, on track for a 3.1 percent weekly decline. It has slipped more than 7 percent from a high of $6,970 on Sept. 5 but is up by about 18 percent this year.
TECHNICALS: Support was between $6,300 and $6,400 around the 50-day moving average and the high point of prices in 2015.
STOCKS: Inventories in LME-registered warehouses registered their biggest weekly inflow since May, rising 67,600 tonnes to 276,025 tonnes and exerting downward pressure on prices. <MCUSTX-TOTAL>
SPREADS: Rising stocks helped to push the discount for cash copper over the three-month contract <MCU0-3> to above $40 a tonne, its highest since December 2009. This suggests that more metal will be delivered over the coming days.
Discounts on cash aluminium, nickel and lead to their three month contracts were at or near multi-year highs. <MAL0-3> <MNI0-3> <MPB0-3>
Cash zinc, however, traded at a premium to three-month metal for the first time since February on concerns over immediate availability after mine closures in China.
CHINA: A rare flurry of disappointing data suggested the Chinese economy is finally starting to lose some momentum. Demand for metals in China should, however, remain strong, ABN AMRO's Burgering said.
U.S. FACTORIES: Industrial production fell 0.9 percent in August, missing expectations.
CHINA OUTPUT: China's non-ferrous metal output fell to a one-year low in August.
MARKETS: Share prices edged lower and the U.S. dollar weakened after North Korea fired a second missile over Japan and U.S. retail sales fell unexpectedly. A weaker U.S. currency makes dollar-denominated metals cheaper for non-U.S. investors.
NICKEL: LME nickel, used in stainless steel production, was 0.6 percent lower at $11,135 a tonne, its weakest since Aug. 21, after Chinese steel prices clocked up their biggest weekly loss since early June.
TECHNICALS: Nickel has fallen more than 10 percent from a high of $12,380 on Sept. 4. Fibonacci support was at $10,965 and $10,530, Marex Spectron brokers said in a note.
LEAD: Lead prices were supported by falling inventories in warehouses monitored by the Shanghai Futures Exchange, which declined by 44.5 percent from last Friday to 16,568 tonnes. LME lead was up 1.8 percent at $2,350 a tonne.
PRICES: Aluminium was down 0.7 percent at $2,083.50 a tonne, zinc was 0.9 percent higher at $3,033.50 and tin gained 0.2 percent to $20,570.
(Additional reporting by James Regan; Editing by David Goodman)