JAKARTA, Dec 8 (Reuters) - Indonesia aims to launch initial public offerings for the upstream and geothermal units of state energy firm Pertamina next year to fund expansion, a senior government official told parliament.

Pertamina Hulu Energi, the upstream unit of Pertamina, is expected to sell a 10% to 15% stake in an IPO next year and had conducted initial "sounding out" of potential investors, Pahala Mansury, deputy minister of state-owned enterprises, told lawmakers on Wednesday.

The government also aims to conclude the IPO of Pertamina's geothermal unit in the first quarter of next year after it was delayed due to "less than optimum" market conditions this year, Pahala said.

The IPO of Pertamina Geothermal Energy was initially targeted to take place in the second quarter of this year.

On Thursday, two sources with knowledge of the matter told Reuters that Pertamina Hulu Energi's IPO could raise up to $2 billion. Citigroup, Credit Suisse and JPMorgan are joint bookrunners with Indonesia's BRI Danareksa and Bank Mandiri, according to a term sheet seen by Reuters.

Indonesian equities have outperformed this year, with the main index up 2.5% on relatively strong economic growth.

However, the performance of large IPOs has been disappointing. PT GoTo Gojek Tokopedia TBK raised $1.1 billion from its IPO earlier this year but its share price has plunged by 70% as investors shun loss-making tech stocks.

Pahala did not give details of the expected fundraising in parliament.

He said in coming years the upstream unit was expected to spend $4 billion to $6 billion a year amid a push by the government to enhance energy security and Pertamina Hulu could not only rely on its parent company.

The government was also preparing for the share sales of state palm oil company Perkebunan Nusantara and state fertiliser maker Pupuk Kaltim, he said. (Reporting by Fransiska Nangoy in Jakarta and Scott Murdoch in Sydney, Additional reporting by Yantoultra Ngui, Editing by Ed Davies and Anshuman Daga)