The campaign for Manhattan district attorney is taking on a more contentious tone as the time dwindles for candidates to accentuate their strengths and highlight their opponents’ weaknesses.

Three candidates are running in the Sept. 15 Democratic primary to succeed retiring District Attorney Robert M. Morgenthau, who has held the job for 35 years. The contenders are Richard M. Aborn, a managing partner at Constantine Cannon; Leslie Crocker Snyder, a partner at Kasowitz, Benson, Torres & Friedman; and Cyrus R. Vance Jr., a partner at Morvillo, Abramowitz, Grand, Iason, Anello & Bohrer.