Sections 68-601 to 68-631 and any amendments thereto shall, except as otherwise provided in this section, be applicable to metropolitan utilities districts and employees and appointees of metropolitan utilities districts. The state agency contemplated in such sections is authorized to enter, on behalf of the State of Nebraska, into an agreement with any authorized agent of the United States Government for the purpose of extending the benefits of the Federal Old Age and Survivors’ Insurance system, as amended by Public Law 761, approved September 1, 1954, to the appointees and employees of each metropolitan utilities district, and all of the appointees and employees covered by a contributory retirement plan are hereby declared to be a separate group for the purposes of referendum and subsequent coverage. Metropolitan utilities districts are hereby declared to be political subdivisions as defined in section 68-602, and the Governor is authorized to appoint the board of directors of any metropolitan utilities district as the agency designated by him or her to supervise any referendum required to be conducted under the Social Security Act and is authorized to make any certifications required by the act to be made to the Secretary of Health and Human Services.