A jury was selected Thursday for Raymond Buckey's second trial in the McMartin Pre-School child molestation case, the longest and costliest criminal proceeding in U.S. history. The seating of 12 regular jurors and six alternates came less than a month after attorneys began their inquiry to find panelists unbiased by publicity surrounding the first Buckey trial. Opening statements were set for Monday. Buckey, 31, who has been a defendant for nearly seven years, was acquitted of 40 molestation charges Jan. 18, and his mother, Peggy McMartin Buckey, was acquitted of 12 charges. But prosecutors decided to retry Buckey on eight counts on which the jury deadlocked. A total of 13 charges were unresolved by that jury, but the prosecution dropped five of those counts. The first trial lasted nearly three years and cost $13 million. The eight remaining charges being tried involve three children who attended the now defunct McMartin preschool in Manhattan Beach _ a dramatically diminished group compared to the hundreds once described as alleged victims. Buckey and his lawyers, who had hoped for dismissal of all remaining charges, have accused District Attorney Ira Reiner of playing politics with the case. They say he decided to retry Buckey to further his own ambitions to become California attorney general. Reiner has denied any ulterior motives. Parents of McMartin school children campaigned loudly to have Buckey retried in the week after his acquittal on most charges. They conducted a letter-writing campaign, went on national TV talk shows and held press conferences to espouse their views. Deputy District Attorneys Joe Martinez and Pam Ferrero have said they hope the new trial can be concluded in six months. But Superior Court Judge Stanley Weisberg warned prospective jurors at the outset that the trial could continue into 1991.