The Air Transport Assn. said traffic for September was up 4.6% from September, 1984 . . . The Investment Company Institute reported that the assets of the nation's 352 money-market mutual funds fell $308.3 million in the week ended Oct. 16 . . . The Los Angeles Department of Water and Power reported that electric production for the week ended Oct. 12 declined 0.08% from the previous week and 6.1% from a year earlier.