Waterville's native son George J. Mitchell H '83, former Senate majority leader, peace broker for Northern Ireland and current chair of the United States Olympic Committee's Ethics Committee and a Special USOC Commission, will be Colby's commencement speaker on May 23, President Cotter announced in March. Mitchell, who worked on summer grounds crews on Mayflower Hill before going down Route 201 to pursue undergraduate studies in Brunswick, earned a law degree at Georgetown University. Currently he is special counsel to the firm of Verner, Liipfert, Bernhard, McPherson and Hand in Washington.     Among those who will receive honorary degrees this year are two husband-and-wife couples: CNN's prime anchor and senior correspondent Judy Woodruff and her husband, Al Hunt, the executive Washington editor of The Wall Street Journal and a Capital Gang panelist on CNN; and outgoing chair of Colby's Board of Trustees Larry Pugh '56 and his wife, Jean Van Curan Pugh '55. Other honorary degree recipients will be Maine's independent governor Angus S. King Jr. and genetic cancer-research pioneer Patricia Davis Murphy '68. Mitchell already received an honorary doctor of laws degree from Colby, in 1983.     For sheer numbers this will be the largest commencement in Colby's 186-year history. Between 515 and 520 graduates will march in the ceremony, eclipsing classes numbering in the 480s in 1989 and 1993. Registrar George Coleman says there are countless subtle factors that determine the number of graduates in each class and that resulted in the record size of the Class of 1999--among them recent increases in Colby's enviable graduation rate. "I've been on the ad hoc committee trying to figure out how to even out the numbers for 33 years," he said.