WARWICK, R.I. — A Superior Court judge has turned down the state’s request to add municipal governments, school districts and scores of other defendants to a lawsuit that challenges the 2011 overhaul of Rhode Island’s pension system.

The law, which raised the retirement age, created investment-style retirement plans and suspended annual cost-of-living adjustments, was designed to save the state $4 billion, but public-sector unions and retirees sued.