Omnicom, Group, the largest of Madison Avenue’s agency holding companies and the parent of OMD and PHD, Tuesday reported net income of $236.5 million for the fourth quarter of 2004, a 12 percent increase from the fourth quarter of 2003. Worldwide revenues rose 11 percent to $2.789 billion. Net income for full year 2004 increased 15% to $723.5 million, while revenues jumped 13 percent to $9,747.2 million.