In international news, a Roman Catholic Church newspaper alleged yesterday that the highest circles of power in Mexico were behind the 1994 murder of ruling party presidential candidate Luis Donaldo Colosio. The archdiocese of Mexico said, in an unusual, outspoken editorial in its publication, that the Colosio slaying was clearly a plot and not the work of a lone gunman. Colosio was the PRI candidate, and he was campaigning in Tijuana when he was gunned down.