The Illinois State Employees Association Retirees sued state officials and retirement systems to block a plan that reduces pension benefits to fix a $100 billion shortfall.

The plan violates the Illinois constitution's guarantee that benefits of any state pension or retirement system "shall not be diminished or impaired," according to a complaint filed yesterday in state court in Springfield, Illinois.

Illinois lawmakers last month approved a bill designed to rescue the nation's worst-funded public-employee retirement system and restore the credit standing of the nation's fifth- largest state. The bulk of the plan's $160 billion in savings over 30 years will come from limits on annual cost-of-living allowances and raising the retirement age for some workers.