A new government report says teen birth rates have declined in Minnesota and the nation as a whole in the first half of this decade. Minnesota participated in the trend and historically has teen birth rates significantly lower than the nation's as a whole. However, African American teen pregnancy rates in Minnesota are among the highest in the nation. Those numbers are NOT declining, even though THEY ARE nationally. Minnesota Public Radio's Bill Catlin reports: Teen birth rates declined from 1990 to 1996 nationally, to about 55 per one thousand 15 to 19 year old females. IN the first half of the 90's Minnesota's teen birth rate dropped 13 percent, a bigger drop than the national decline of 8 and a half percent. Rebecca Wright saw some of the trends a