WASHINGTON – Is the Libya war legal? Under the 1973 War Powers Resolution, it is not. President Obama has exceeded the 90-day period to receive retroactive authorization from Congress.

But things are not so simple. No president should accept – and no president from Nixon on has accepted – the constitutionality of the WPR, passed unilaterally by Congress over a presidential veto. On the other hand, every president should have the constitutional decency to get some congressional approval when he takes the country to war.

The model for such constitutional restraint is – yes, Senator Obama – George W. Bush. Not once but twice (Afghanistan and then Iraq) did Bush seek and receive congressional authorization, as his father did for the Gulf War. On Libya, Obama did nothing of the sort. He claimed exemption from the WPR on the grounds that America in Libya is not really engaged in “hostilities.”

To deploy an excuse so transparently ridiculous isn’t just a show of contempt for Congress and for the intelligence of the American people. It manages additionally to undermine the presidency’s own war-making prerogatives by implicitly conceding that if the Libya war really did involve hostilities, the president would indeed be subject to the WPR.

The worst of all possible worlds: Insult Congress, weaken the presidency. A neat trick.

But the question of war-making power is larger than one president’s blundering. We have a core constitutional problem. In balancing war-making power between Congress and the presidency, the Constitution grants Congress the exclusive right to declare war.

Problem is: No one declares war anymore. Since World War II, we’ve been involved in five major wars, and many minor engagements, without ever declaring war.

But it’s not just us. No one does. Declarations of war are a relic of a more aristocratic era, a time when, for example, an American secretary of state closed his department’s code-cracking office because “gentlemen do not read each other’s mail.”

The power to declare war has become, through no fault of anyone, archaic and obsolete. Taken literally, it is as useless as granting Congress the right to regulate horse-and-buggies.

We need, therefore, some new way to fulfill the original constitutional intent. The WPR was a good try, but it failed because it was the work of Congress alone, which tried to shove it down the throat of the Executive, which, in turn, for over three decades has resisted it as an encroachment on the inherent powers of the commander in chief.

Moreover, the judiciary, which under our system is the ultimate arbiter of constitutionality, has consistently refused to adjudicate this “political question” (to quote one appellate court judge) and thus resolve with finality the separation-of-powers dispute between the other two co-equal branches.

We therefore need a new constitutional understanding, mutually agreed to by both political branches, that translates the war-declaration power into a more modern equivalent:

First, formalize the recent tradition of resolutions (Gulf, Afghanistan, Iraq) authorizing the initiation of war and recognize them as the functional equivalent of a declaration of war.

Second, establish special procedures for operations requiring immediacy and surprise, for example, notification of the House speaker, Senate majority leader and their opposition counterparts, in secret if necessary.

Third, in such cases, require retroactive authorization by the full Congress within an agreed period – but without any further congressional involvement (contra the War Powers Resolution). The Constitution’s original grant of power to Congress was for a one-time authorization, with no further congressional constraint on executive war-making except, of course, through the power of the purse.

The Libya adventure is too much of a mess to expect mutual agreement on this kind of constitutional compromise now. Nor is Obama, having bollixed the war powers issue in every possible way, the man to negotiate this deal.

Resolution of this issue will require time, dispassion and therefore inevitably a commission – say, chaired by a former president of each party, Bill Clinton and George W. Bush, and consisting of former legislators, judges and generals, with perhaps a couple of historians and not more than one international lawyer thrown in.

Then submit the commission’s proposed new law for approval by Congress and the president. And have David McCullough read the final text aloud at the signing ceremony. That will make it official.

We need a set of rules governing the legality of any future war. This will allow us to concentrate on the most important question: its wisdom.

© 2011, The Washington Post Writers Group