In a ruling that called into question nearly two centuries of presidential “recess” appointments that bypass the Senate confirmation process, a federal appeals court ruled on Friday that President Obama violated the Constitution when he installed three officials on the National Labor Relations Board a year ago.

The ruling was a blow to the administration and a victory for Mr. Obama’s Republican critics — and a handful of liberal ones — who had accused him of improperly asserting that he could make the appointments under his executive powers. The administration had argued that the president could decide that senators were really on a lengthy recess even though the Senate considered itself to be meeting in “pro forma” sessions.

But the court went beyond the narrow dispute over pro forma sessions and issued a far more sweeping ruling than expected. Legal specialists said its reasoning would virtually eliminate the recess appointment power for all future presidents at a time when it has become increasingly difficult to win Senate confirmation for nominees.

“If this opinion stands, I think it will fundamentally alter the balance between the Senate and the president by limiting the president’s ability to keep offices filled,” said John P. Elwood, who handled recess appointment issues for the Justice Department during the administration of President George W. Bush. “This is certainly a red-letter day in presidential appointment power.”

The Constitution, written at a time when it could take weeks for members of Congress to get to the capital, allows presidents to fill vacancies temporarily during recesses for positions that would otherwise require Senate confirmation. In recent years, as senators have frequently balked at consenting to executive appointments, that authority has served as a safety valve for presidents of both parties.

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