Employees Retirement System of Rhode Island, Providence, is extending past Jan. 1 the contracts of custodian State Street Bank and Pacific Corporate Group, an alternative investment adviser. Although the contracts of the firms have already expired, trustees of the $6.5 billion fund will review the firms post-Y2K, said a spokesman for Treasurer Paul Tavares. Mr. Tavares and other trustees of the $6.5 billion fund also approved the policy of waiting to conduct manager searches until Y2K fears and realities have been resolved. Money manager changes would be made this year only if an investment firm were found not to be compliant by the Sept. 30 deadline. Managers seem to be prepared so far, the spokesman added.