* Copper cash-to-three backwardation eases to $50/T
* Shanghai copper premiums slip to $105-125/T
* China traders jittery on financing after Qingdao probe
(Updates prices, adds comment, detail; previous SYDNEY)
LONDON, June 4 (Reuters) - Copper prices fell to a three-week low on Wednesday, pressured by signs of a surplus and doubts about the outlook for demand from China, with traders concerned about disruption to import shipments related to a probe of financing deals.
Benchmark copper on the London Metal Exchange (LME) slid to a session low of $6,765 a tonne, its lowest level since May 12. At 1035 GMT, it was down 1.4 percent lower at $6,770 a tonne.
The premium for cash copper over three-month prices <CMCU0-3> has fallen from last week's two-year high of $101 a tonne to $50 on Wednesday, indicating that market tightness has been easing.
"The market expected that any available metal would disappear into China's state reserve. But in the last week following state purchases, there has been a drop in premiums for delivery into China," Nic Brown, head of commodities research at Natixis said.
"That tells me that the market is not as tight as it was."
A Reuters poll in July showed analysts expected the copper market to be in a 228,000 tonne surplus this year, with that number rising to 262,000 tonnes in 2015.
China's economy has had a bumpy ride this year as a run of data has showed a cooldown in investment, retail sales and factory output, feeding concerns that growth could fall further from an 18-month low seen between January and March.
While a private sector survey showed an improvement in China's factory activity, overall factory growth was still contracting, undermining confidence that the country is getting back on track, said Helen Lau, a mining analyst at UOB-Kay Hian Securities in Hong Kong.
"The overall economy is mixed, not on a firmer footing ... and at the same time summer is around the corner when fabrication rates at (copper) cable plants will start to slow," she said.
"We are not surprised to see this consolidation."
Also reducing appetite for copper, China's northeastern port of Qingdao halted some shipments of aluminum and copper last week due to an investigation by authorities.
Copper premiums in Shanghai fell on Wednesday after traders cited concerns over disruptions to some shipments at China's third-largest port of Qingdao, related to a probe into the use of the metal as collateral in financing.
Looking further ahead, a key U.S. jobs report on Friday is expected to show that job growth slowed in May and the unemployment rate probably ticked up, but not by enough to upset the view that the economy is bouncing back strongly after a winter slump.
Aluminum fell to its lowest level in a week at $1,817 a tonne in intraday trade, before paring losses to trade down 1.3 percent at $1,821.25 a tonne.
The discount for cash aluminum versus three-month prices fell to an 18-month low of $22 a tonne on Tuesday before rising to a $24.25 discount on Wednesday.
"This (narrowing contango) is a bearish factor for premiums as it reduces the attractiveness of financing deals," Harbor Aluminum Intelligence Unit said in a note.
Aluminum premiums in Europe are trading at record highs of around $400 a tonne, largely underpinned by financing deals in aluminum that lock away vast amounts of the metal away from consumers.
In industry news, foreign copper miners in Indonesia have agreed in principle to pay a controversial export tax, the country's deputy finance minister said, following a series of talks aimed at restarting concentrate exports after a near-five-month halt.
New Caledonia, which this week allowed Brazil's Vale to restart its nickel operations after an acid spill and subsequent riot, is not open to new mining plants, having reached maximum capacity, an influential and newly elected local government official told Reuters.
Three month LME copper
Most active ShFE copper
Three month LME aluminum
Most active ShFE aluminum
Three month LME zinc
Most active ShFE zinc
Three month LME lead
Most active ShFE lead
Three month LME nickel
Three month LME tin
(Additional reporting by Melanie Burton in Sydney; editing by Jane Baird)