The department shall prepare a state plan in accordance with the provisions of 42 U.S.C. 1396 - 1396p (Title XIX, Social Security Act, Medical Assistance) and submit it for approval to the United States Department of Health and Human Services. The plan shall designate that the Department of Health and Social Services is the single state agency to administer this plan. The department shall act for the state in any negotiations relative to the submission and approval of the plan. The department may make those arrangements or regulatory changes, not inconsistent with law, as may be required under federal law to obtain and retain approval of the United States Department of Health and Human Services to secure for the state the optimum federal payment under the provisions of 42 U.S.C. 1396 - 1396p (Title XIX, Social Security Act, Medical Assistance).