A lot of us who have voiced bafflement and frustration about President Bush's success in selling his logic for a war against Iraq have been strangely silent about the constitutionality of such an undertaking. We've behaved as though the question of war is a matter of presidential discretion.

Well, it isn't -- or at any rate, it shouldn't be. It's right there in the Constitution -- Article I, Section 8 -- that Congress, not the president, has the power to declare war. Nor do I find anything to suggest that Congress may delegate its war-making authority to the president.

And yet the assumption is that the war on Iraq will begin when the president wants it to begin -- perhaps with a heads-up to Congress that it has happened. Almost everyone I know assumes that it's the president's call. The war hawks assume it, the latter-day peaceniks assume it, Congress itself assumes it. Which probably means that it is, at least in practical terms, a fact.

Not a particularly reassuring fact, however. Leaders of Congress are old enough to recall the Gulf of Tonkin Resolution that laid the (phony) rationale for President Johnson's escalation of the conflict in Vietnam -- another war Congress never got around to declaring. I suspect a few Americans wish Congress hadn't been so quick to roll over for LBJ. Are there no similar misgivings today?

But it isn't Bush's rationale for war that concerns me here, although it seems no less phony than Johnson's. It is the constitutional legitimacy of it.

One might argue that, given the evolution of war since Article I was written -- the ability of nations now to strike quickly, across great distances and with devastating power -- the American president needs the authority to respond instantaneously, without congressional debate.

But the seemingly inevitable war on Iraq is not an emergency of the sort that got us into World War II, our last declared war. The nearest thing to a Pearl Harbor-like sneak attack on the United States was Sept. 11, 2001, which, despite Bush's efforts to have us believe otherwise, had next to nothing to do with Iraq. Whatever military action we take against Iraq and its hated leader, Saddam Hussein, will be the result of sober calculation over a considerable time. In those circumstances, why shouldn't Congress invoke its constitutional prerogative?

One possible answer is that Bush, in response to his critics, took the matter out of congressional hands when he brought it before the United Nations. Iraq's offenses, he argued there, were offenses against the United Nations, not against the United States per se. He made a strong case that future defiance on Saddam Hussein's part should prompt a military response from the United Nations. But Bush didn't get everything he sought at the United Nations. He wanted language that, in effect, made military action automatic upon a finding of material breach of the agreements Iraq had signed.

Some argue that America's power to make war really resides in the White House -- in what Vice President Cheney has described as an "inherent presidential power" to defend "vital national interests" -- no matter what it says in the Constitution. That's one possible explanation of why Bush won't seek a congressional declaration of war. Another may be his recollection that the 1991 resolution to approve military action by the elder Bush against Iraq -- which, remember, had occupied Kuwait and had been condemned as an international aggressor by the United Nations -- passed the Senate by only five votes.

The rationale would be weaker this time -- essentially that Iraqi violation of the U.N. resolutions will be ample ground for a U.S. assault on Baghdad. Maybe the younger Bush is afraid the votes wouldn't be there -- though I can't imagine why. This has been such a rollover Congress -- not, I suspect, because members support the president's determination to go to war but because opposing it is the more controversial posture.

The trend of recent years has been for politicians to avoid controversy when possible. Candidates would rather attack an opponent's proposals than make any of their own. Most controversial legislation passed at the state and local level seems to have come by way of referendum -- with no politician having to take a strong public position.

So I don't imagine the men and women of our national legislature will step forward and tell the president that, under the separation of powers, declaring war is a congressional responsibility. I just think they ought to.