Washington ? There was a time when conservatives fought passionately to preserve America as a limited constitutional republic. That was, in fact, the essence of conservatism. It’s one reason Franklin Roosevelt’s vast expansion of government through the New Deal aroused bitter opposition on the right.

But many conservative advocates seem to have lost that philosophical commitment. They now advocate autocratic executive rule, largely unconstrained by constitutional procedures or popular opinions.

This curious attitude is evident in the conservative response to the gnawing question: Where are Saddam Hussein’s weapons of mass destruction? A surprising number of conservatives respond: So what? He must have had them; maybe he gave them away. And, anyway, Hussein was a bad guy. In their view, even to ask the question is to mount a partisan attack on President Bush, and that’s downright unpatriotic. It always seemed likely that Baghdad possessed weapons. Not only did Iraq once maintain a weapons program, but how else to explain the regime’s obstructionist behavior during the inspections process?

Yet it made equal sense to assume a desperate Hussein would use any weapons of mass destruction to defend his regime — and that serious elements of Baghdad’s arsenal would be quickly found.

There may be a logical explanation for the fact that WMD were not used and have not been located; significant weapons stockpiles might eventually turn up.

Moreover, it’s hard to imagine the administration simply concocting its weapons claims. The president, though a practiced politician, isn’t the type to lie so blatantly. Whatever the faults of his lieutenants, none seems likely to advance a falsehood that would be so hard to maintain.

But the longer we go without any discoveries, the more questionable the prewar claims appear to have been.

So it is entirely fair to ask the administration: Where are the weapons of mass destruction? The answer matters for the simplest practical reasons. Possible intelligence failures need to be corrected. Washington’s loss of credibility should be addressed; saying “trust me” will be much harder for this president in the future or a future president.

Stonewalling poses an even greater threat to our principles of government. It matters whether the president lied to the American people. Political fibs are common, not just about with whom presidents have had sex, but also to advance foreign-policy goals. Remember the Tonkin Gulf incident and inaccurate claims of Iraqi troop movements against Saudi Arabia before the first Gulf War?

Perhaps the administration manipulated the evidence, choosing information that backed its view, turning assumptions into certainties, and hyping equivocal materials. That, too, would hardly be unusual. But no president should take the nation into war under false pretenses. There is no more important decision: The American people deserve to hear official doubts as well as certitudes.

The point is not that the administration is necessarily guilty of misbehavior, but that it should be forced to defend its decision-making process.

Pointing to substitute justifications for the war just won’t do. Deputy Defense Secretary Paul Wolfowitz notes that the alleged al-Qaida connection divided the administration internally, and humanitarian concerns did not warrant risking American lives. Only fear over Iraqi possession of weapons of mass destruction unified the administration, won the support of allies, particularly Britain, and served as the centerpiece of the administration’s case. If the weapons didn’t exist, or were ineffective, Washington’s professed case for war collapses.

Conservatives’ lack of interest in the question takes an even more ominous turn when combined with general support for presidential war-making. Republicans — think President Eisenhower, for instance — once took seriously the requirement that Congress declare war. These days, however, Republican presidents and legislators, backed by conservative intellectuals, routinely argue that the chief executive can unilaterally take America into war.

Thus, in their view, once someone is elected president, he or she faces no legal or political constraint. The president doesn’t need congressional authority; Washington doesn’t need UN authority. Allied support is irrelevant. The president needn’t offer the public a justification for going to war that holds up after the conflict ends. The president may not even be questioned about the legitimacy of his professed justification. Accept his word and let him do whatever he wants, irrespective of circumstances.

This is not the government created by the founders. This is not the government that any believer in liberty should favor.

It is foolish to turn the Iraq war, a prudential political question, into a philosophical test for conservatism. It is even worse to demand unthinking support for Bush. He should be pressed on the issue of weapons of mass destruction — by conservatives. Fidelity to the Constitution and republican government demands no less.