In spite of a campaign to make August a "murder-free" month in Kansas City, Mo., 15 homicides were recorded, the most for any month this year. In an average month, the city of 430,000 has about nine slayings. But a decline in less serious assaults led some organizers, such as City Councilwoman Carol Coe, to say the effort should continue. Assaults declined most sharply among young people, the group that the murder-free month sponsors tried to reach with radio spots, billboards, street theater, workshops and sermons. Lucile Bluford, publisher of the local black newspaper, The Call, urged continuing the campaign with less ambitious goals. "Can we push for a murder-free week?" she mused.