“ In keeping with our duty to avoid deciding constitutional questions presented unless essential to proper disposition of a case, we look first to petitioners' nonconstitutional claim that respondent acted in excess of powers granted him by Congress. Generally, judicial relief is available to one who has been injured by an act of a government official which is in excess of his express or implied powers. ”

“ This brings us to the merits. The Solicitor General conceded that if the District Court had jurisdiction to review respondent's determinations as to the discharges he issued these petitioners and if petitioners had standing to bring these suits, the action of respondent is not sustainable. On the basis of that concession and our consideration of the law and this record we conclude that the actions of the Secretary of the Army cannot be sustained in law. ”

“ An authoritative construction of the congressional grant of power is to be found in the regulations of the Department of the Army. Army Regulation 615-375, par. 2 (b) states: 'The purpose of a discharge certificate is to record the separation of an individual from the military service and to specify the character of service rendered during the period covered by the discharge.' (Emphasis supplied.) Moreover, the Army's Regulation 615-360, par. ”