Mieczyslaw Rakowski, the Deputy Premier who has emerged as a trusted associate of General Wojciech Jaruzelski's, is one of the country's ablest and most prominent figures, yet remains one of the most enigmatic. In his 24-year career as editor in chief of the weekly newspaper Polityka, Rakowski, 55, projected the image of that rarest of Communists: a candid advocate of political and economic reform.