Senators Dean G. Skelos, R-Rockville Centre, and Pedro Espada, D-Bronx, had challenged the July 8 naming of Mr. Ravitch as the state’s second-in-command. Mr. Paterson appointed Mr. Ravitch, a former head of the Metropolitan Transportation Authority, as a way of breaking a monthlong leadership deadlock in the state Senate.

Justice LaMarca said the senators demonstrated a “likelihood of success on the merits for their claim that neither the constitution nor legislative enactment authorized the governor to make the appointment.” He noted that the governor’s legal team conceded at oral arguments last week that Mr. Ravitch is “presently performing the duties of lieutenant-governor,” including serving as president of the Senate and as a member of various committees. Were Mr. Paterson “to die, resign, or be removed from office, Mr. Ravitch, if allowed to remain in office, is next in the line of succession,” Justice LaMarca wrote. He concluded that allowing an allegedly “illegally appointed lieutenant-governor to act as governor of the state would clearly constitute irreparable harm.”