Monday July 27, 1998
   Kellie Martin, a veteran of such TV shows s Life Goes On and Christy, may need a sedative when she reports to work for her latest gig: ER.   "I'm going to be very starstruck my first day," says Martin, 22, who will play a third-year med student when the hit NBC drama returns for its fifth season.   "It's the only show I watch, I want to meet [George] Clooney just because he's a hottie. Not that Eric [La Salle] and Noah [Wyle] aren't!"   Martin, who will defer her senior year at Yale to do ER, is already boning up for her role.   "I have a lot of friends who are in med school, so I've been asking them a lot of questions," she says.   "I always said, 'I never want to play a doctor or a lawyer, because they have to say too many big words.' I hope I can remember the dialogue when I hit an artery on a patient and the blood starts shooting out."