The F-B-I reports serious crime has declined nationwide for the sixth consecutive year. The Bureau's figures, released over the weekend, aren't broken down by specific state or region, but as Minnesota Public Radio's Michael Khoo reports, Minnesota is in line with the national trend. NARRATION: The F-B-I's Uniform Crime Reporting Program shows the number of both violent and property crimes fell in 1997 -- down two percent from the year before and seven percent from five years ago. Justice Department spokesman Nicholas Gess says there's no single factor to account for the downward trend. GESS: Primary among them are President Cl