The $7 billion Illinois State Universities' Retirement System, Champaign, will offer an alternative defined contribution plan in the next year, said CIO Kenneth E. Codlin. Participants may decide whether to join the new plan or stay in the defined benefit one. Under legislation passed last year, state retirement systems in Illinois may establish defined contribution plans alongside existing defined benefit plans. The system will retain control of investment management of the defined contribution plan, which will be employer directed. Other details still are being worked out. Mr. Codlin wouldn't discuss possible investment managers or asset allocation for the new plan.