In order to extend to employees of the state and its political subdivisions and to the dependents and survivors of such employees, the basic protection accorded to others by the old-age and survivors insurance system embodied in the Social Security Act, it is hereby declared to be the policy of the general court, subject to the limitations of this chapter, that such steps be taken as to provide such protection to employees and officials of the state and its political subdivisions on as broad a basis as is permitted under the Social Security Act, except as may be otherwise specifically limited herein. It is also the policy of the legislature that the protection afforded employees in positions covered by a retirement system on the date an agreement under this chapter is made applicable to service performed in such positions, or receiving periodic benefits under such retirement system at such time, will not be impaired as a result of making the agreement so applicable or as a result of legislative enactment in anticipation thereof.