SINGAPORE, Feb 6 (Reuters) - Singapore state investor Temasek Holdings [TEM.UL] said on Friday its chief executive Ho Ching will step down and be replaced by former BHP Billiton CEO Chip Goodyear on Oct. 1.

Ho Ching, wife of Prime Minister Lee Hsien Loong, joined Temasek as a director in January 2002 and has been CEO since January 2004.

"The team has already embarked on a different stance since mid-2007, and has begun to review its long-term plans under different scenarios prompted by the economic downturn," Chairman S. Dhanabalan said at a media briefing.

"If we are to bring in new leadership, it would be just as good a time as any to involve a new leader in this review."

Goodyear, 51, stepped down as CEO of BHP Billiton in January 2007. He joined Temasek's board on Sunday.

Temasek, which had S$185 billion ($123.2 billion) in assets as at March 2008, has been hit hard due to its 40 percent exposure to banks that have slumped in value due to the global financial crisis.

The sovereign wealth fund's key investments include 28 percent of DBS Group (DBSM.SI), just under a fifth of Standard Chartered Bank (STAN.L) and about 3.8 percent of Bank of America (BoA) (BAC.N) following BoA's takeover of Merrill Lynch.

Temasek's $5 billion plus investment in Merrill alone has resulted in a loss of more than $2 billion. [ID:nBNG274629] (Reporting by Kevin Lim and Saeed Azhar, Editing by Ian Geoghegan)