BEIJING (Reuters) - For China, the trade dispute raised this week with the West may in retrospect seem minor compared to the ructions that await Beijing as its state firms start to punch their weight on global commodity markets.

The U.S. and EU complaint to the World Trade Organization accuses China of unfairly restricting exports of several metals such as zinc, steelmaking ingredient coke and bauxite, the raw material for aluminum; at the same time India and Australia complained about Chinese firms dumping cheap aluminum goods.

Both are the result of China using tried and tested tax or tariff policies to ensure resource supplies and protect domestic industry. But as its domestic demand begins to outstrip its own resource base, those policies will become less effective.

For commodity markets, the concern is that Beijing could utilize its growing trade network and strategic stockpiles as its next best lever to protect its economy.

"I think the lesson learned over the last two years was that China was very much the price taker, in the sense it was more supply sensitive rather than price sensitive. Hence you have this massive commodity boom," said Mark Pervan of ANZ Bank.

"I suspect it will be a different in the next 10 years with China much more heavily involved in the global market."

"China is effectively the new boy in town, a very big boy, and realizing it can throw its weight around. But it needs a major education process and a better regulatory environment to avoid creating massive volatility."

China's state-owned firms don't have a particularly illustrious history in international markets. An apparently rogue short position on copper roiled the London Metal Exchange in 2005; oil prices fell sharply in late 2004 as the offshore unit of trader China Aviation Oil nearly collapsed under a $550 million trading loss.

But that isn't stopping Beijing from taking action to see that it has some influence on the trade of commodities, allowing it either to soften the impact of its expanding demand or to profit from it.

If its steel industry fails to reach a deal in the next week with stubborn miners for lower iron ore prices, it could mark the end of a decades-old system of annual contracts; PetroChina (0857.HK) has hired traders in Houston and London and this week closed a $1 billion acquisition in Singapore that will give it a powerful position in the oil pricing hub for Asia.

China is also grooming the Agricultural Bank of China to be a world player in grains trading, and has teamed up with Japanese firms in a move that will give it more expertise in agricultural markets, where it is expected to become a major player eventually as its food demand exceeds local supply.

Having been stung before, China may take a more cautious approach to trading, particularly with heightened scrutiny of commodity market speculation and manipulation in the West. But the latest trade disputes show that even relatively modest change in China has the potential to cause big waves.

"I think China's commitment to a free-trade regime is greater than people give the country credit for, but that they will use trade tariffs to tweak economic policy," said Ben Simpfendorfer, China economist at RBS in Hong Kong.

WEIGHT, BACKED BY RESERVES

China taking a growing share of global commodity demand is nothing new, but the slow-down in developed economies against the relative resilience of China has accelerated it.

Although China leads world production in a few commodities such as manganese -- a steel ingredient and one of the subjects of the U.S. and EU complaint -- the pace of growth in the past decade means demand for many materials outstrips production.

China's response to the crisis has been a huge credit loosening and a government spending plan, coupled with a campaign to buy resources, buoying prices and making China the main or only driver of demand for many global commodity markets.

China now buys more than half the world's iron ore; it now produces less than half its own crude.

And unlike the past five-year boom that caught Beijing as off guard as the rest of the world, it has sizeable inventories of copper, aluminum, crude oil and iron ore, having taken advantage of the slump to stock up.

And it is building up a larger supply buffer with deals to buy mines in Australia and oilfields abroad, like Sinopec's $7.2 billion bid for Addax Petroleum (AXC.TO).

TRADE SPAT

The latest trade disputes also show how China is caught in a double-bind, blamed for not supplying enough of certain resources and too much of others, with winners and losers on both sides.

While firms in some U.S. and European markets are hungry for more Chinese imports, others say they are gagging and want their governments to turn off the tap.

U.S. steelmakers have complained about China flooding the market with a type of steel tubes used in oil drilling and the European Union slapped a 24 percent anti-dumping duty on Chinese imports of wire rod, another steel product, on Tuesday.

India imposed a 14 percent duty on Chinese aluminum flat products on Tuesday and Australia launched an investigation into extruded aluminum on Wednesday.

"If the United States prevails, it is not a win-win," says Lyle Vander Schaaf, an international trade attorney with Bryan Cave LLP in Washington. "There will be U.S. producers of commodities who will lose U.S. market share to producers in China."

(Additional reporting by Jonathan Leff)