MILAN, April 13 (Reuters) - Generali investor Fondazione CRT said on Wednesday it supported the plan for the Italian insurer put forward by challenger shareholder Francesco Gaetano Caltagirone.

Fondazione CRT, a Turin-based banking foundation, said in a statement it liked Caltagirone's plan because of its "ambitious and sustainable growth objectives" for Generali.

Generali, Italy's biggest insurer and a cornerstone of the financial system, is at the centre of a shareholder battle that has called into question the reappointment of CEO Philippe Donnet.

Caltagirone, who is the second biggest investor in Generali behind investment bank Mediobanca with a holding of more than 9%, has challenged the decision by Generali's board to hand Donnet a new term at the helm. Mediobanca backs Donnet.

The two sides will face off on April 29 when investors vote to name a new board.

Caltagirone can count on the support of fellow magnate Leonardo Del Vecchio, who owns around 8% of Generali.

Fondazione CRT, which holds 1.7% of Generali, had struck a shareholder pact with the two billionaires that was later dissolved to avoid drawing regulatory scrutiny.

Earlier on Wednesday, Caltagirone's CEO candidate told La Stampa daily in an interview there was room to increase Generali's debt leverage above the current 20%, and bridge part of the gap with rival Allianz's 25%, if needed to pursue worthwhile deals.

(Reporting by Federico Maccioni, editing Maria Pia Quaglia and Valentina Za, Kirsten Donovan)