For years, the St. Louis school district has experienced the convergence of two trend lines school superintendents hope never to see: rising employee-pension costs and falling student enrollment. Despite years of fully funding its share of the teacher-pension plan, the proportion of the St. Louis district's budget tied up in paying benefits for its teachers now makes up about 10 percent--a factor that, coupled with other rising costs, is fueling ongoing cuts in this beleaguered district. St. Louis' situation has resonance far beyond the city, because its troubles are similar to those that other districts are likely to face. In St. Louis, many of the cuts have been shaped with input from the city teachers' union. Changes to the pension structure have not yet been made, but they have been proposed, and more are likely to be on the table in the future. "The current system is no longer sustainable by the district," said Steven R. Carroll, the school system's lobbyist in the state capital.