* Production restarts, to push up supplies
* LME stocks could hit 5 million tonnes by Q3
* Power costs could boost aluminium prices by end-2009
By Pratima Desai
LONDON, June 8 (Reuters) - A tug-of-war in the aluminium market is likely to end in victory for the bears because prices are expected to buckle under the weight of supplies, stocks and bleak demand prospects.
Over the longer term though, aluminium could be sustained by power, estimated to account for about one-third of output costs. For some smelters the number can be as highs as 50 percent.
Earlier this year the market saw a large build up of short positions -- bets on lower prices for the metal used in power and construction. But analysts say in recent weeks the trend has shifted towards long positions.
"The macro-based indiscriminate rally ... has resulted in aluminium becoming the most dislocated from fundamentals... making it our favoured metal to short at current levels," said Gayle Berry, analyst at Barclays Capital.
Aluminium has jumped about 16 percent to 5-month highs near $1,600 a tonne on the London Metal Exchange since May 28 on expectations of a demand recovery and Chinese stockpiling.
But analysts say stocks in London Metal Exchange warehouses, at record highs above 4.27 million, a gain of nearly half a million tonnes since May 1, are a sign of severe weakness.
"We are seeing very large inventory increases, which doesn't give you any confidence that this market is anywhere close to rebalancing," said Adam Rowley, analyst at Macquarie Bank.
"The problem with any bullish view on aluminium are signs that some producers are restarting capacity mainly in China."
Overall, analysts estimate about 8.5 million tonnes of production capacity around the world had been shut.
IN THE SHOP WINDOW
However, a stronger price performance on the LME and in China, the world's largest producer, has triggered restart of output capacity previously closed.
"We believe that about 1.6 million tonnes-per-year of capacity is in the process of being restarted and an additional 500,000 tonnes-per-year of new capacity is firing up," said Barclays Capital's Berry.
"Unless one believes that consumption is expanding fast enough to absorb this additional metal, then the Chinese market is in danger of moving into a large surplus."
A recent Reuters survey showed analysts expect the aluminium market surplus to jump about 1.7 million tonnes and demand to shrink by nearly 6 percent.
Reinforcing the bearish case are some expectations that stocks in LME warehouses could by the third quarter reach 5 million tonnes -- more than 10 percent of the market estimated at around 37 million tonnes.
Alex Heath, head of base metals trading at RBC Capital Markets said a lot of aluminium which had stayed outside LME warehouses was now finding its way in because producers needed the cash.
"It's in the shop window now as opposed to being in the garage," he said. "The market has got ahead of fundamentals ... But it is still very short."
The weight of short positions as seen in open interest -- nearly 830,000 lots or more than 20 million tonnes -- on LME aluminium contracts shows many still expect lower prices.
But this collective short exposure could mean a price spike in the event these positions have to be bought back.
POWER CONTRACTS
Over the longer term, however, many citing higher energy costs expect a firmer foundation under higher aluminium prices.
Many smelters get their power under contract, so for now the price surge may have little impact. But these contracts will at some point have to be renegotiated.
"Electricity costs in China are still low, but soon power producers will be asking aluminium smelters for more," said Eugen Weinberg, analyst at Commerzbank.
"At the end of the year we will see clear signs of recovery and it's possible aluminium prices could be 20 percent higher by December ... Right now the market is playing a "V" shaped recovery, I don't buy this."
But there is a caveat -- China's State Reserves Bureau has to stop buying aluminium, which could weigh on prices in Shanghai and stop local smelters from reactivating capacity and possibly prompt more shutdowns. (Editing by James Jukwey)