By Angeliki Koutantou and John Stonestreet ATHENS (Reuters) - The leader of Greece's conservatives signalled on Tuesday he would step down as the party seeks to recover from the shock of a heavy election defeat that pollsters failed to predict. New Democracy said it would hold a leadership election as soon as possible after losing to the leftist Syriza party. Vangelis Meimarakis, who shepherded the party through Sunday's ballot, said he was unlikely to stand.