A federal judge in New York yesterday ordered the Reagan administration to move as quickly as possible to begin spending $21.85 million on a solar conservation program that the administration had wanted to kill.

U.S. District Court Judge Charles S. Haight told the administration to expedite activities of the congressionally-created Solar Bank, designed to provide subsidized financing to lower and moderate income families who install solar and energy conservation measures, and ordered Housing and Urban Development Secretary Samuel R. Pierce Jr. to submit affidavits specifying what will be done and when in time for a hearing Sept. 2

But Haight sidestepped the legal issues underlying the suit, dismissing the question of whether funds had been illegally impounded by Reagan and Cabinet officials. He also refused to adopt a specific timetable for spending the money, as he had been asked to do by plaintiffs in the suit, who included the Solar Lobby, individual consumers, representatives of the solar industry and five members of Congress.

The lawsuit had charged that Reagan illegally withheld money from a program that Congress had mandated and funded while a request to Congress to wipe out funding for the program was pending.

Lawyers for the Solar Lobby and the Natural Resources Defense Council argued that Reagan and five Cabinet secretaries "ignored all statutory deadlines and congressional commands" by reassigning the personnel responsible for getting the bank going, terminating consultants who were assisting the start-up activities, refusing to convene a meeting of the bank's advisory committees and failing to issue required reports. When the lawsuit was filed, plantiffs said that no money appropriated for the bank this fiscal year had been spent.

U.S. Justice Department attorneys said that the administration is now proceeding to implement the program, a switch that the plaintiffs' lawyers said was caused by the lawsuit.

But the Justice Department said the impoundment issue was moot since the administration had taken action to obey Congress's mandate after the request for recision of funds failed.

Judge Haight apparently agreed, dismissing that argument and removing Office of Management and Budget Director David A. Stockman from the list of defendants.