* Aluminium stocks in LME warehouses fall to lowest since March 2008
* GRAPHIC-2018 asset returns: tmsnrt.rs/2jvdmXl (Adds official prices)
By Zandi Shabalala
LONDON, Sept 26 (Reuters) - Copper fell for a third straight session on Wednesday as the dollar firmed ahead of clues on the direction of U.S. interest rates later in the day following an expected hike.
Benchmark copper on the London Metal Exchange edged down 0.7 percent to $6,271 per tonne in official open outcry activity.
With the Federal Reserve widely expected to raise interest rates on Wednesday, financial markets are focused on whether signs of an acceleration in U.S. economic growth will prompt the central bank to ramp up the pace of monetary policy tightening.
"The market is waiting for any commentary that suggests a potential change to forward guidance and the impact on the dollar," said ING commodities strategist Warren Patterson.
A stronger greenback makes dollar-denominated commodities more expensive for non-U.S. firms, a relationship used by funds to generate buy and sell signals.
But Patterson said that copper market fundamentals were "looking quite constructive" as demand from top consumer China was robust and inventories of the metal continued to fall this year.
DOLLAR: The dollar gained 0.2 percent against a basket of its peers before an expected Federal Reserve interest rate hike priced in by investors, who are still on edge about a trade row between the United States and China.
TRADE CONCERNS: Persistent concerns over tit-for-tat trade tariffs between China and the United States are denting demand for risky assets, such as metals.
CHINA PREMIUMS: Premiums for metal on the physical market in China are at $117.50 a tonne, up nearly 40 percent since August. CU-BMPBW-SHMET
STOCKS: LME copper inventories MCUSTX-TOTAL inched slightly higher to 212,925 tonnes, but were still near the lowest since January.
CHINA DEMAND: China's underlying demand for refined copper remained resilient, driving global copper demand, Argonaut Securities analyst Helen Lau said.
ALCOA UNION: The union at Alcoa's aluminium operations in the state of Western Australia said it was meeting the company again on Wednesday to try to resolve a strike that has lasted more than six weeks, after the firm last week revised an earlier offer.
ALUMINIUM STOCKS: Stocks in LME-monitored warehouses fell below a million tonnes for the first time since March 2008 on Wednesday, at 999,925 tonnes. MALSTX-TOTAL
OTHER METALS: LME aluminium was bid 0.4 percent higher at $2,080 per tonne, zinc traded 0.7 percent higher at $2,525 a tonne, lead was bid up 0.2 percent at $2,013 a tonne, tin was bid at a steady $18,900 a tonne, while nickel was bid up 0.2 percent to $12,975 a tonne.
Additional reporting by Manolo Serapio Jr.; editing by Louise Heavens and Adrian Croft