* Some investors taking profits - ABN AMRO
* Inventories register biggest weekly inflow since May
* LME/ShFE arb: http://bit.ly/2wZSAEz (Adds closing prices)
LONDON, Sept 15 (Reuters) - Copper was steady on Friday, helped by a weaker dollar but still recorded its biggest weekly price fall since March as investors took profits from a speculative rally to three-year highs.
While some investors booked profits, supply deficits and solid demand for metals in top consumer China were expected to keep prices around current levels, ABN AMRO analyst Casper Burgering said.
COPPER: Benchmark copper on the London Metal Exchange ended at $6,508 a tonne, up 0.1 percent on the day and down 2.8 percent this week. It has slipped from a three-year high of $6,970 on Sept. 5 but is still up 18 percent so far 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 putting 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 more metal will be delivered over the coming days.
Discounts on cash aluminium, nickel and lead to their three month contracts also rose to multi-year highs. <MAL0-3> <MNI0-3> <MPB0-3>
But cash zinc 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. But demand for metals in China should remain strong, ABN AMRO's Burgering said.
OUTPUT: China's non-ferrous metal output fell to a one-year low in August.
MARKETS: Share prices and the U.S. dollar edged lower after North Korea fired a second missile over Japan. A weaker U.S. currency makes dollar-denominated metals cheaper for non-U.S. investors.
NICKEL: LME nickel, used in stainless steel production, closed down 0.9 percent at $11,090 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 rose 2.3 percent to $2,359 a tonne.
PRICES: Aluminium fell 0.6 percent to $2,085 a tonne, zinc added 0.9 percent to close at $3,039 and tin was unchanged at $20,540.
(Additional reporting by James Regan; Editing by David Goodman and Edmund Blair)