New York City Comptroller William C. Thompson, who oversees $75.1 billion in assets for the citys five pension funds, is working with the trustees of all the funds to expedite diversification of their existing portfolios, said Jeff Simmons, spokesman. The plans are aimed at improving performance in the face of rising pension costs. Mr. Thompson projected pension expenses will increase over the next several years to $1.8 billion in fiscal 2003; $2.5 billion in fiscal 2004; $3.1 billion in fiscal 2005; and $3.8 billion in fiscal 2006. The funds lost 8.3% for fiscal year 2002, ended June 30. Further details werent available.