Joe Clark, the controversial educator who a week ago announced his impending resignation as principal of Eastside High School in Paterson, N.J., is coming to Hollywood to guest star on an episode of "227," NBC's half-hour sitcom about family life in a black neighborhood in Washington. On the episode, to be taped April 11 for possible airing the following week, Clark will play himself and encourage a high school drop-out to resume his education. The show is part of NBC's "The More You Know" campaign which focuses on education and emphasizes the value of teachers in society. Although Clark is known for his colorful speech and multi-syllabic words, his part will be scripted. Still, "227" executive producer Irma Kalish expects Clark to inject something of himself into the role. "He is of course very flamboyant and very expressive. I have a feeling that he's going to be doing some rewriting of our script."