* Some investors taking profits - ABN AMRO
* Copper poised to finish 2.9 pct down on the week
* Inventories register biggest weekly inflow since May
* LME/ShFE arb: http://bit.ly/2wZSAEz (Updates throughout, changes dateline from Sydney)
LONDON, Sept 15 (Reuters) - Copper prices steadied on Friday, helped by a weaker dollar, but were set for their biggest weekly fall since March as investors took profits from a speculative rally to three-year highs.
While ABN AMRO analyst Casper Burgering said that some investors were taking profit, he added that supply deficits and solid demand for metals in top consumer China is expected to keep prices around current levels.
COPPER: Benchmark copper was up 0.1 percent at $6,505 a tonne at 1052 GMT but was still down 2.9 percent this week. The metal used in power and construction has fallen 7 percent from a high of $6,970 on Sept. 5 but has gained about 18 percent this year.
TECHNICALS: Support was between $6,300 and $6,400 at 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, 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 also rose to 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 that the world's biggest metals consumer is finally starting to lose some momentum as borrowing costs rise.
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 in as many weeks. A weaker U.S. currency makes dollar-denominated metals cheaper for non-U.S. investors.
NICKEL: LME nickel, used in stainless steel production, was down 1.1 percent at $11,075 a tonne, the lowest 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: Inventories in warehouses monitored by the Shanghai Futures Exchange fell by 44.5 percent from last Friday to 16,568 tonnes, supporing prices. LME lead was up 1.5 percent at $2,343 a tonne.
PRICES: Aluminium was down 0.1 percent at $2,097 a tonne, zinc rose 0.6 percent to $3,024.50 and tin gained 0.2 percent to $20,580.
(Additional reporting by James Regan; Editing by David Goodman)