METALS-London copper slips as U.S. impasse erodes risk appetite
* IMF downgrades global growth forecast
* Aluminium premiums fall due to LME "confusion" - Alcoa
* Yunnan Tin Co chairman charged with bribery by China
(Adds detail; updates prices)
LONDON, Oct 9 (Reuters) - London copper dropped on Wednesday to a three-session low as the U.S. fiscal deadlock corroded desire for risk, with markets further dissatisfied by the prospect that any increase in the country's debt ceiling will be short-term.
The saga over budget disagreements dragged on well into its second week, leaving investors reluctant to trade in an uncertain atmosphere.
"Copper is now a victim of the general risk of default," said Gianclaudio Torlizzi, partner at T-Commodity.
"As long as these uncertainties on the U.S. front continue, traders will reduce risk because they fear some kind of margin call might happen."
Benchmark copper lost 0.65 percent to $7,192 a tonne by 0922 GMT.
In a face-off with Republicans on Tuesday, U.S. President Barack Obama refused to give way over the opposition's demand for budget concessions, saying he would negotiate only if they agree to re-open the federal government and unconditionally raise the debt ceiling.
Market uncertainty was unabated by Obama's hint that he might accept a short-term increase in the ceiling to avoid default.
"This is not something that the market will like, because it will increase uncertainty," Torlizzi said.
The global economy also lost ground, as the International Monetary Fund on Tuesday downgraded its 2013 global growth forecasts to 2.9 percent from a July estimate of 3.1 percent, due to softening growth in developing economies.
Aluminium producer Alcoa Inc's chief financial officer said on Tuesday that global aluminium premiums have fallen due to "confusion" over the London Metal Exchange's proposal to overhaul its warehousing policy.
Alcoa and Russian producer Rusal have called on the LME to release more detailed data on long and short positions as well as inventories, and want the exchange to delay a decision on the long-running issue.
Benchmark aluminium gained 0.6 percent to $1,875.5 a tonne, zinc rose 0.6 percent at $1,896.5, and lead edged up 0.2 percent at $2,098.
Nickel ticked down 0.2 percent to $13,868 a tonne, while tin lost 0.1 percent to $23,525 a tonne, but remained near a seven-month high, supported by a Friday spike on worries over supplies from top exporter Indonesia.
The chairman of Yunnan Tin Co, the world's largest tin producer, was earlier arrested by Chinese authorities and charged with accepting bribes, in the latest example of the country's recent anti-corruption drive.
China markets were back for a second day after a week of holidays.
(Editing by Dale Hudson)