Kevin Mitchell's calling card once read "criminal investigator," when his days and nights brought him to the scene of burglaries, assaults and any other felonies or misdemeanors reported to the sheriffs department in Buffalo, Wyo. Now his professional mission is nothing less than spearheading a battle for survival of a sparsely populated school district that is trying to counter the crushing forces of demographics and finance. Mitchell's role as superintendent of the 700-student Big Horn School District 1, located along Wyoming's northern frontier, does not differ much from that of any other school district leader in rural America today. But the native of Casper, Wyoming, has extended his assignment voluntarily to lead statewide advocacy for public schools in the state's legislative and legal arenas.