Trustees of the $21.7 billion Virginia Retirement System, Richmond, decided to change the leadership of the investment and real estate committees every two years, said Bill Sullivan, a spokesman. Starting in July, Alice W. Handy will become chairman of the fund's investment committee, replacing Gordon Binns Jr. Ms. Handy, treasurer of the University of Virginia at Charlottesville, has been vice-chair of the committee. At the same time, Robert C. Butcher Jr., president of Builder Resource and Development Co., will take over from James S. Watkinson as head of the pension fund's real estate committee. Messrs. Binns and Watkinson will continue to serve on their respective committees.