Dan M. Slack was named executive director of the Illinois State Universities Retirement System, Champaign, which has $13.4 billion in defined benefit assets and $341 million in 401(a) assets. The board of trustees announced its decision today after a national search to replace James M. Hacking, who resigned in August to become administrator of the $5.9 billion Arizona Public Safety Retirement System, Phoenix. Executive recruiter DHR International assisted the board in the search. Mr. Slack, associate executive director and general counsel, had been an interim executive director since Mr. Hacking left. Information on how Mr. Slack's two positions will be filled was not available.