In order to extend to employees of the state and its political subdivisions and of the instrumentalities of either, 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 this state, subject to the limitations of Articles 1 and 3, that such steps be taken, and they are hereby expressly authorized, as to provide such protection to employees of the state and its political subdivisions and of the instrumentalities of either on as broad a basis as is permitted under applicable federal law. 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 article 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.