Vermont's three statewide public retirement plans issued joint RFPs for two S&P 500 index managers to run a combined $500 million; one will run an enhanced portfolio and the other an equal-weighted fund. The $1.2 billion State Teachers' Retirement System, $1 billion State Employees' Retirement System and $218 million Municipal Employees' Retirement System are considering investing up to 80% of each plan's large-cap domestic equity allocation in passive strategies, compared with less than 30% for each currently, said David Minot, Vermont's director of finance and investment services. State Treasurer Jeb Spaulding said the potential fee savings from coordinating the strategy of the three plans is another factor behind the move. Officials for the plans hope to review responses and make selections by mid-December. New England Pension Consultants is advising.