Trustees of the $37 billion Ohio Public Employees' Retirement System, Columbus, may increase the fund's exposure to equities to 35% of assets, said Joel S. Buck, investment officer. The fund now has 26% of assets in domestic equities, and a small portion in international stocks. An asset allocation study by Wilshire Associates, due next month, is expected to recommend the increased stock exposure. The money would come from cash, he said. The fund manages all of its domestic equity allocation in-house.