(Reuters) - U.S. President-elect Donald Trump is considering retired General David Petraeus, who resigned as CIA chief in 2012 after an extra-marital affair was revealed, is being considered for the post of defense secretary, the Wall Street Journal reported on Friday, citing people with knowledge of the transition process. Also under consideration as Pentagon chief are retired Marine General James Mattis, retired Army General Jack Keane, former national security adviser Stephen Hadley and former Senator Jim Talent, the Journal said. Keane said on Twitter on Friday that he will not be joining the new administration. 