The preliminary hearing for Cathy Evelyn Smith, the Canadian woman accused of murder in the 1982 drug death of comedian John Belushi, was postponed until June 17 to give her lawyer time to locate and subpoena witnesses. Attorney Howard L. Weitzman said in Los Angeles Municipal Court that he may seek the testimony of April Milstead, the woman who allegedly arranged for Smith to provide heroin to Belushi, and of Milstead’s friend, Charles W. Pearson. Both are believed to be in the Washington, D.C., area. Outside the courtroom, Weitzman said Smith may take the stand in her own defense. Judge Brian Crahan ordered Weitzman and Deputy Dist. Atty. Michael Montagna to return to court May 7, when attorneys for several writers who have been subpoenaed in the case are expected to argue that their clients should not be forced to appear.