New Delhi, July 14: Ajay Prasad, who was officer on special duty to Deputy Prime Minister L K Advani, today took over as defence secretary. He replaces Subir Dutta, who has taken over as member of Union Public Services Commission. A 1969 batch IAS officer of the Himachal Pradesh cadre, Prasad had earlier held the post of additional secretary in the ministry of defence, a defence ministry spokesman said. Bureau Report