CLOSING THE BELUSHI CASE

Even as she admitted injecting John Belushi with heroin-and-cocaine ''speedballs'' on the night before his death in 1982, onetime Singer Cathy Evelyn Smith, 39, insisted she was innocent of murder. Smith and her lawyers argued that as Belushi's companion in his final days, she had acted at the 33- year-old comedian's urging. In Los Angeles last week, Smith's legal battle ended in a compromise. Prosecutors dropped a second-degree murder charge against the Canadian-born defendant in exchange for her plea of no contest to a count of involuntary manslaughter and three counts of administering and furnishing narcotics to Belushi. Instead of a possible 25 years to life, she faces a maximum of eight years and eight months. Deputy District Attorney Elden Fox conceded that the accused ''honestly believes from a moral standpoint that she is not responsible for his death.'' Still, he will push for a three-year prison term. Said Fox: ''Cathy Smith is paying far less of a price for her participation (in drug abuse) than John Belushi did.''