Elsztain to invest up to $100 mln in parent of IDB Holding

* Elsztain to invest $25 mln for 10 pct of Ganden

* Has option to invest up to $75 mln more

TEL AVIV, Sept 23 (Reuters) - Argentinian businessman Eduardo Elsztain signed an agreement to invest up to $100 million in Ganden Investments, the parent company of debt-strapped Israeli conglomerate IDB Holding Corp.

According to the agreement, Elsztain will invest $25 million in Ganden for a 10 percent stake and get an option to invest an additional sum of up to $75 million. If the option is exercised fully, Elsztain will hold 30.8 percent of Ganden, IDB said in a statement on Sunday.

Last week IDB said there were advanced talks for an investment to be made by Elsztain in Ganden, the private company through which IDB Chairman Nochi Dankner controls IDB.

The investment would provide much-needed cash for IDB, which has been selling off assets in recent months to reduce its hefty debts. This month it reported a huge second-quarter loss that raised concerns it may not be able to pay its debts and included a "going concern" warning in its quarterly results.

Elsztain is chairman and chief executive officer of IRSA , Argentina's biggest real estate company. He also serves as chairman of Cresud , a major agriculture producer with 35 farms and 1 million hectares under management in Argentina, Brazil, Paraguay and Bolivia.

The IDB group, which has assets of $30 billion, controls Cellcom, Israel's leading mobile phone operator, supermarket chain Super-Sol and Clal Insurance . Its subsidiary Koor Industries owns a 2.4 percent stake in Credit Suisse. (Reporting by Tova Cohen)