AMERICAN CABLESYSTEMS <ACN> TO BUY CABLE SYSTEM American Cablesystems Corp said it agreed in principal to buy a cable television system in Los Angeles County from Heritage Communications Inc <HCI> for 15.5 mln dlrs. The company said the system being purchased serves about 12,000 subscribers in the towns of Compton, South El Monte, Hawaiian Gardens and the communities of Willowbrook, Athens, Firestone, Florence and East Compton. It said the acquisition will bring to seven the number of cable systems it owns, manages or has agreed to buy in the Los Angeles area.