MANILA - San Miguel Corp is in talks to buy a stake worth about $500 million in Adaro Energy, Indonesia's largest coal producer by market value, the Philippine conglomerate's president said on Wednesday.

It will be the second time that San Miguel has attempted to buy a stake in an Indonesian coal firm, after earlier talks to take a majority stake in the Southeast Asian country's top miner PT Bumi Resources (BUMI.JK) fizzled out.

Yes, in talks with Goldman, San Miguel president Ramon Ang told Reuters when asked if Southeast Asia's biggest food and beverage firm was among possible buyers of the stake up for sale in Adaro.

Ang declined to say how big a stake San Miguel plans to buy.

Goldman Sachs (GS.N), Citigroup (C.N) and hedge fund Farallon were looking to sell around 17 percent of Adaro Energy to strategic investors, sources told Reuters earlier this month.

The sale was expected after a lockup period ended in March for financial sponsors, which included the three financial groups, which had participated in Adaro's $1.3 billion initial public offering last year, analysts had said.

Goldman Sachs (GS.N), with a 9.94 percent stake in Adaro, is coordinating the sale of the shares, one source with direct knowledge of the matter said two weeks ago.

Goldman Sachs was adviser to San Miguel in the Manila-based conglomerate's ambitious diversification plan, which resulted in San Miguel's purchase of 27 percent of utility Manila Electric Co (MER.PS) last year, a planned telecommunications venture, and a pending purchase of majority of oil refiner Petron Corp (PCOR.PS).

San Miguel is diversifying away from its traditional food and beverage business to fuel future growth.

Analysts said investors may want to sell out of Adaro given the uncertainty over coal prices amid an economic downturn.

(Reporting by Rosemarie Francisco, editing by Will Waterman)