By Ben Blanchard

BEIJING (Reuters) - Leaders from five of the world's top emerging economies will discuss a coordinated stance on economic issues such as commodity price fluctuations, but the yuan's exchange rate is off the agenda, a senior Chinese diplomat said on Saturday.

The mid-April "BRICS" summit will gather leaders from China, Russia, India, Brazil and South Africa in the southern Chinese beach resort of Sanya.

The summit is unlikely to achieve much concrete, though it will give the world's big rising economies a venue to coordinate views on global financial reforms, commodity prices and other shared concerns.

"The BRICS countries have similar concerns or stances on important questions like the global economy, international finance and development," Assistant Chinese Foreign Minister Wu Hailong told a news conference.

"We hope all sides can strengthen coordination and mutual cooperation on reform of the international currency system, commodity price fluctuations, climate change and sustainable development," he added.

"This is a topic at the G20 summit in Cannes and ... the leaders of the five countries will exchange views on this," he added. "We hope that the five countries' leaders can have a joint stance on this issue and reach a broad consensus."

But Wu said the Chinese currency's exchange rate would not be talked about at the Sanya summit. Some countries say China keeps the yuan artificially undervalued to help boost Chinese exports.

"The renminbi's exchange rate is not on the agenda for discussion," he said, repeating China's standard line that its currency was not the cause of global imbalances.

China's hard work at perfecting the yuan's exchange rate mechanism was "clear for all to see," he added. Renmibi is the yuan's formal name.

Brazilian government officials have said they want to discuss the issue of the yuan, whose cheap value they say has helped fuel a flood of Chinese imports and deteriorated Brazil's trade balance.

The BRICS group has emerged as a loose united front to press the rich Western economies, especially the United States, which has traditionally dominated global diplomacy.

Yet there are many disparities among the BRICS member countries, and the past two summits of the evolving group have not achieved much. This time, too, strains over China's currency policies and trade surpluses could make real agreement even harder to reach.

The leaders may also discuss Libya and the broader situation in the Middle East.

"It would be natural if the leaders discussed this issue, but at the moment we have not heard that any country has said they wish to make a dedicated statement on it," Wu said.

China, with Russia, India, Brazil and other developing countries have condemned the U.S.-led air strikes on Libyan forces. South Africa, on the other hand, voted in favor of the United Nations Security Council resolution authorizing the air strikes.

(Editing by Jeremy Laurence)