And yet, the court added, “We would expect such a momentous decision to be preceded by substantial debate, and expressed in unmistakable language” by Congress.

Steven Aftergood, the director of the Federation of American Scientists’ Project on Government Secrecy, said the appeals court ruling reflected the tensions between what he portrayed as the executive branch’s instinctive secrecy about national security and the need for open debate if the war on terror is to be permanent.

“Over time, it becomes a question of what is it that we are protecting,” he said. “Are we protecting simply physical security and our geographical boundaries, or are we protecting a system of political values? That includes open deliberation of national security policies. And for many people it is the latter. It’s not that physical security is unimportant. But it is a means to an end, and the end is an open society that includes vibrant debate.”

A range of officials involved with the phone records program since its secret creation by the Bush administration in October 2001 gave similar explanations for their repeated reluctance to go to Congress for explicit authorization. Permitting public debate about the program, the current and former officials said, would have tipped off the enemy and reduced its value as a wartime tool.

“When you put something out there and have a debate, terrorists get an alert, so the question is, how publicly are you going to do this?” said Robert L. Deitz, who was general counsel of the N.S.A. from 1998 to 2006. “That is a nice thing for a terrorist to know because they can take countermeasures. To my mind, all these questions come down to, what is the trade-off between transparency and security?”

The appeals court ruling was just one example of the pressures on the executive branch to disclose information about national security policy to the public.

Last year, a different three-judge panel on the Second Circuit ruled that the Obama administration had to make public Justice Department memos about the scope and limits of the executive branch’s claimed power to target and kill an American citizen deemed a terrorist.