* ICICI, Temasek, Metavante stakes at valued at $220 million

* Buyer will need to launch public offer for extra 20 percent

* Shares extend gains to more than 5 percent (Adds details, share reaction)

By Narayanan Somasundaram & Indulal P.M

HONG KONG/MUMBAI, Nov 9 (Reuters) - India's ICICI Bank (ICBK.BO: Quote, Profile, Research), Singapore's state investor Temasek Holdings [TEM.UL] and another large shareholder have revived plans to sell their stakes in back-office company Firstsource Solutions (FISO.BO: Quote, Profile, Research), in a deal valued at $285 million at the current market price, sources said.

ICICI, Temasek's Aranda Investment and U.S.-based banking technology group Metavante own a combined 68 percent of Firstsource and have hired Citigroup (C.N: Quote, Profile, Research) to arrange the deal, the sources with direct knowledge of the deal said on Monday.

The sources declined to be named as they were not authorised to speak to the media.

The news pushed Firstsource shares to a session high of 37.35 rupees or 5.4 percent. By 0922 GMT, the shares were up 3 percent in a firm Mumbai market .BSESN

ICICI shares extended gains to over 5 percent on the news.