These rules-- 1. Set forth the requirements and procedures for certain individuals under age 65 to enroll and become entitled to Medicare Part A benefits through payment of monthly premiums; 2. Revise the rules on State buy-in for Medicare benefits to provide that-- After 1988, a State may, at any time, request a buy-in agreement or a modification of an existing agreement, including a modification under which the State may enroll a pay Part B premiums on behalf of a new buy-in coverage group--Qualified Medicare Beneficiaries (QMBs); and After 1989, a State may request and obtain a modification of an existing agreement, under which the State may also enroll QMB's in Part A and pay Part A premiums on their behalf. These amendments are necessary to conform HCFA rules to changes made by section 9010 of the Omnibus Budget Reconciliation Act of 1987 (OBRA '87), section 301 of the Medicare Catastrophic Coverage Act of 1988 (MCCA), and sections 6012 and 6013 of the Omnibus Budget Reconciliation Act of 1989 (OBRA '89). The purposes of the amendments are-- 1. To make it possible for certain disabled individuals to become entitled to Medicare Part A benefits that require payment of a monthly premium. The provisions apply to an individual under age 65 who loses entitlement to Medicare Part A without premiums because his or her earnings exceed the limit imposed for entitlement to social security disability benefits, on which Medicare Part A entitlement was based; and 2. To make available to States, for payment of premiums for QMBs, the administrative and cost efficiencies of the State buy-in procedures.