The battle over President Bush’s warrantless eavesdropping program has faded as a political issue. But it serves to illustrate a legal principle that should be — but has not been — a point of consensus in the broader debate about presidential war powers.

The principle is that while the president should have power during an extraordinary emergency to temporarily disregard outdated laws that may impede his ability to protect American lives, that power should lapse once he has had time to seek appropriate congressional changes in the laws.

I call this the emergency-powers principle. Its logic has been overlooked by many Bush critics as well as supporters in assuming their respective positions: that the eavesdropping program either was illegal from the outset (as critics claim), or has always been legal and will always be immune to congressional regulation (as defenders claim).

The better view is that Bush was right to start the eavesdropping program (assuming that the still-secret details show the need for it) during the post-9/11 emergency — but was wrong to keep its existence secret and to resist congressional regulation.

Although various laws give the president extraordinary powers during emergencies, no general emergency-powers principle is spelled out in the Constitution or in any judicial decision that I can find. But the principle is implicit in the Framers’ division of powers between Congress and the president.

It is also compelled by common sense. In the days and weeks after the 9/11 attacks, the administration had reason to fear that more attacks might be imminent. It also had cause for concern that the Foreign Intelligence Surveillance Act — badly outdated by new communications technologies and by the vastly enhanced terrorist threat — might make it unduly difficult to find the plotters.

The commonsensical response to this situation was pithily (and thus anonymously) articulated to me by a senior Clinton administration lawyer: "If I had been advising the president on September 12, the legal doctrine that I would have invoked is, ‘Mr. President, f**•FISA.’ "

So perhaps we should not fault either the National Security Agency’s immediate initiation of new surveillance that stretched its previously cautious interpretation of FISA or the president’s subsequent order that the agency disregard some of FISA’s clear requirements.

Remaining secret are the details, the precise timing, and Bush’s exact actions. But it appears likely that the administration’s timetable was too fast to allow for advance consideration by Congress. Even the rushed enactment of the USA PATRIOT Act (including several FISA amendments) took 46 days, during which the NSA should have been pulling out all the stops to find terrorists.

But contrary to Bush critics such as Sen. Russell Feingold, D-Wis., and to many Bush defenders, the premise that the president’s emergency powers justified disregarding FISA in the wake of the 9/11 attacks does not require the conclusion that he was free to disregard FISA forever.

Feingold, who claims that the Bush program was illegal from the start, has suggested that otherwise, "FISA is a dead letter, all of the supposed protections for civil liberties contained in the reauthorization of the PATRIOT Act … are a cruel hoax, and any future legislation we might pass regarding surveillance or national security is a waste of time and a charade."

Many Bush defenders use somewhat similar logic. They leap from the premise that Bush was surely right to trump FISA after 9/11 to their usual conclusion that he has virtually unlimited "inherent" wartime power to disregard any and all laws that he considers inconvenient.

(Bush defenders also argue that Congress’s post-9/11 vote authorizing a military response implicitly amended FISA to give him sweeping surveillance powers.)

So it is that Feingold and other critics, fearing that the president will become too strong for years or decades to come, would make him too weak to deal effectively with emergencies. And Bush’s defenders, fearing that the president will be too weak to deal with emergencies, would give him virtually unlimited powers for as long as he says that the nation is at war.

The emergency-powers principle should quiet critics’ fears by making it clear that allowing the president extraordinary powers in an emergency does not mean that he retains those powers after Congress has had time to consider a response.

(For a more ambitious proposal to create an "emergency Constitution" without resorting to the prescribed amendment process, see Before the Next Attack, a recent book by professor Bruce Ackerman of Yale Law School.)

This logic marries the Framers’ plan to make Congress the pre-eminent policy maker — in time of war as well as peace — with their understanding that only the president would be able to react to unanticipated crises with the necessary dispatch.

The Constitution assigned to Congress both the legislative power and the power to initiate wars. (See my August 31, 2002, column, "An Invasion of Iraq Requires the Approval of Congress.") It assigned to the president both the executive power and the command of the armed forces. This included the power to "repel sudden attacks" when there is not time for Congress to deliberate and vote on a course of action, as James Madison said in his notes taken at the 1787 Constitutional Convention.

The emergency power to repel sudden attacks necessarily includes the power to conduct whatever surveillance may help anticipate such attacks before Congress has had time to react. But this does not mean that presidential power trumps congressional power indefinitely in all matters of foreign intelligence surveillance.

Rather, it means that when emergency conditions convince the president that congressional restrictions on his powers are dangerously outdated, he should be able to temporarily suspend compliance. But he should also have a corresponding duty to notify Congress of his actions; to seek new legislation ratifying them; and to comply with any restrictions that Congress attaches to the new legislation (assuming a congressional override of any veto).

This is what President Lincoln did after unilaterally suspending the writ of habeas corpus in April 1861 to round up Confederate sympathizers in Baltimore who had been helping a Southern army that threatened Washington. He later persuaded Congress, the body vested with power to suspend the writ, to ratify what he had done.

President Bush, on the other hand, hid his decision to disregard FISA for more than four years — until it leaked — from all but a handful of congressional leaders, who were sworn to secrecy. This despite FISA’s explicit provision allowing wartime "electronic surveillance without a court order" for only 15 days "following a declaration of war by the Congress." Bush has also resisted calls for new legislation subjecting his program to congressional and judicial oversight. And his lawyers have suggested that any restrictions on his surveillance powers would be unconstitutional.

By these actions, Bush has violated any reasonable understanding of the Constitution’s system of checks and balances.

The appropriate congressional response would be to amend FISA to adapt the 28-year-old statute to technological change and the heightened terrorist threat. The amended version should be fully binding on the president unless and until some new emergency again exposes previously unanticipated problems.

"When the President takes measures incompatible with the expressed or implied will of Congress, his power is at its lowest ebb," as Justice Robert Jackson wrote in a famous 1952 concurrence.

A corollary, in my view, is that when the president temporarily suspends compliance with an arguably outdated expression of Congress’s will, he must at the same time ask Congress to update it and must comply with any updated version.

In this case, it is unclear whether an updated version is in the offing. Despite considerable bipartisan agreement that Bush has overreached, the issue has had little resonance with voters. So Congress may end up acquiescing.

That would be a shame. On a range of issues — also including indefinite detention without due process, torture, and the claimed power to launch pre-emptive invasions without congressional approval — Bush has reached for presidential powers that are both broader than necessary to fight terrorism and dangerous to our constitutional system.

As Justice Jackson warned, "I have no illusion that any decision by this Court can keep power in the hands of Congress if it is not wise and timely in meeting its problems…. We may say that power to legislate for emergencies belongs in the hands of Congress, but only Congress itself can prevent that power from slipping through its fingers."