IT'S HAMMER TIME: Jury selection in the O.J. Simpson case entered its most crucial phase as 300 potentials began to be narrowed down to 12 finalists and eight alternates. Candidates were questioned both by the prosecution and the defense about how much of the case they had been exposed to. Defense attorney Johnnie Cochran Jr. was especially curious about how jurors felt about the police: "Do you understand that it's possible that police can make mistakes?" he asked them. "You understand that doctors, coroners, can make mistakes?" The jury selection will continue through the week until enough candidates are weeded out.