CHICAGO, Oct. 27 — Representative Jesse L. Jackson Jr. said Monday that he would soon endorse Howard Dean for the Democratic presidential nomination, telling a mostly black audience on the South Side of Chicago that Dr. Dean had "the best chance to be the next president of the United States." "I'm not wasting my time with any more non-straight-talking candidates," Mr. Jackson said in introducing Dr. Dean, a former governor of Vermont, to a group of about 150 people at Chicago State University. "I've seen him stand up for health care," he said. "I've seen him stand up for students....