A divided federal appeals court today dismissed a case challenging the National Security Agency’s program to wiretap without warrants the international communications of some Americans, reversing a trial judge’s order that the program be shut down.

The majority in a three-judge panel of the United States Court of Appeals for the Sixth Circuit, in Cincinnati, ruled on a narrow ground, saying the plaintiffs, including lawyers and journalists, could not show injury direct and concrete enough to allow them to have standing to sue.

Because it is extremely difficult to show concrete injury from the highly classified program, the effect of the ruling was to insulate the program from judicial scrutiny in ordinary federal courts.

The majority did not rule on the merits of the case, though the appeals judge who wrote the lead opinion, Alice M. Batchelder, said the case provoked “a cascade of serious questions.” Those questions included whether the program violated a 1978 law, the Foreign Intelligence Surveillance Act, along with the Constitution’s First and Fourth Amendments.