KCBS-TV Channel 2 plans to add a 30-minute noon newscast to its weekday schedule beginning Jan. 4, a spokesman for the CBS-owned station said Wednesday. Anchors for the program have yet to be named but they are likely to come from the station's current roster. The new newscast will bring the station up to three hours of local news programming each day. To make room for the noon broadcast, the station will move "The Young and the Restless" to 11 a.m. and cancel "Slim Cooking with Richard Simmons." In an unrelated move, it was announced that Pat O'Brien would be leaving KCBS effective immediately. O'Brien, hired as an anchor but more recently working as a special assignment reporter for the station, decided not to renew his contract. "He wanted to anchor, we wanted him to do special assignments," a station spokesman said. O'Brien will continue to host his "At the Half" segment seen as part of the network's National Basketball Assn. telecasts.