* Freeport Indonesia says mineral export ban would cut output by 60 pct
* To cost Indonesia $1.6 bln in lost revenue, or 0.6 pct of GDP growth next year
* Says to cut output by 900 mln pounds of copper, 1.7 mln ounces of gold next year
JAKARTA, Dec 12 (Reuters) - Freeport McMoRan Copper & Gold warned that Indonesia's plan to ban mineral exports from next month would cut the firm's revenues in the country by 65 percent, costing Southeast Asia's biggest economy $1.6 billion in lost revenue next year.
From January, mining companies must process ore before shipping it overseas, part of policies aimed at boosting the value of exports of raw materials from Indonesia, the world's top exporter of nickel ore, thermal coal and refined tin.
But a tumbling currency, a precarious trade deficit and protests from industry have made the Southeast Asian nation reconsider the step. Indonesian President Susilo Bambang Yudhoyono is expected to make a final decision soon on the ban.
"We are trying to inform and convince the government how serious this is," Freeport Indonesia CEO Rozik Soetjipto told Reuters.
Last week, lawmakers said they would not dilute the law, adopted five years ago, and it must go ahead as scheduled.
If there are no changes to the ban, Freeport was expected to face a loss in revenue of around $5 billion next year, or 65 percent of its total in Indonesia, due to losses in production from the world's second-largest copper mine.
The U.S. mining giant estimated that output at its Grasberg mine would fall by 60 percent next year, consisting of a cut of 900 million pounds of copper and 1.7 million ounces of gold. It would also have to layoff half of its 15,000 employees in Indonesia.
For Indonesia, that translates into a loss of $1.6 billion in taxes, royalties and dividends, or 0.6 percent of GDP growth. The central bank expects GDP growth of around 6 percent next year, compared to 5.7 percent this year.
"What we are trying to convince government and members of parliament is that allowing us to continue exporting our product would not be breaching the law," Soetjipto said.
Freeport currently processes only around 40 percent of its ore mined domestically at one smelter in East Java, but the prevailing law requires it to smelt all of it in Indonesia from mid-January.
PT Indovasi and PT Indosmelt also plan to build smelters to take ore from Freeport, but construction has yet to start.
(Writing by Randy Fabi; Editing by Ed Davies)