Amending the Constitution, like marriage itself, is an endeavor not to be entered into lightly.

In calling for a constitutional amendment to uphold marriage as a union between a man and a woman, President Bush stressed that his decision to pursue this fateful step was no thoughtless, knee-jerk response. Rather, he noted, the decision reflected the fact that a rash of push-the-envelope activism by state and local officials has left no other option available to resolve the simmering debate over the nature, purpose and legal status of marriage.

The president's announcement has brought a previously defused debate into sharp focus. The argument rages not only between those who would extend marriage to same-sex couples and those who would refuse, but even among the latter group, which is split between those who say an amendment is the way to go and others who insist the issue be left to the states. Yet his debate is just what we need, because how the issue is settled will shape the future of our society and the course of constitutional government in the United States.

What, precisely, has forced the president's hand? A series of geographically dispersed judicial decisions, beginning with a trial court in Hawaii, followed by a Superior Court in Alaska, and then a Vermont Supreme Court ruling. Last November, the Massachusetts Supreme Judicial Court declared that traditional marriage upholds persistent prejudices and that same-sex couples have a fundamental right to marry in their state.

Emboldened by the activism of the Massachusetts bench, San Francisco officials have issued thousands of fraudulent marriage licenses to same-sex couples, intentionally contrary to clear state law, and sued to have a judge declare California's marriage laws discriminatory and unconstitutional in that state. (On Thursday, the California Supreme Court ordered an immediate halt to those marriages and said it would hear arguments in May or June on whether the San Francisco mayor has the authority to allow same-sex marriages.)

Public officials in other states also have shown a regrettable desire to conduct similar legal experiments. A city clerk in New Mexico issued several same-sex marriage licenses before the attorney general of that state intervened to halt this interpretation of state laws. The mayor of New Paltz, N.Y., noting ambiguity in New York law, has performed several same-sex marriages. The mayor of Chicago invited officials in Cook County to consider issuing same-sex marriage licenses. In Oregon, Multnomah County (which includes Portland) is issuing same-sex marriage licenses, while stopping short of performing marriage ceremonies. The list goes on and on.

The effect of these decisions, and the intent of the litigation strategy behind them, is unmistakable: to establish same-sex marriage as a civil right, one that the federal government would then be constitutionally obligated to secure nationwide. Advocates of gay marriage demand, and will accept, nothing less. To reach this outcome, activist judges have disregarded thousands of years of custom and experience, flouting the laws of society, and thumbing their noses at every major religious tradition. A legal preference for traditional marriage is, they decree, "irrational."

What's truly troubling here is the brazen attempt to skirt the democratic process and redefine marriage by judicial fiat. Through their rogue actions, local officials are claiming the power to decide for themselves which laws they will enforce and which they will not. By overriding long-standing majority opinion, disregarding the rule of law and excluding the people from so fundamental a decision as marriage, these judges and officials flagrantly flout the very cornerstones of democracy.

Here's one core principle that should guide the debate from here on: Marriage is a unique institution that is central to the welfare of society - and it must be protected.

Marriage is the formal recognition by society and the laws of society of the most profound relationship that can exist between a man and a woman. Social science tells us that, when you tinker with marriage, children suffer. They suffer when fathers are absent; they suffer when mothers are absent. By virtue of its function and purpose in society, marriage is an essential institution.

But must we amend the Constitution?

I'm reluctant to change our most fundamental law. The Constitution should be amended rarely and only for the most important of reasons. That's why the Founding Fathers made the amendment process so difficult, requiring that two of every three members of the House and the Senate approve a proposed amendment and that it be ratified by three-quarters of the states.

But this is not just another policy disagreement, a curious question fit for social experimentation. Society now faces a concerted legal and political effort to forcefully redefine and thereby undermine one of its most basic institutions. This question can no longer be avoided, and it will not go away.

It is, moreover, a question too fundamental to the good of society to be left up to the states. With most issues, no serious harm results if the states differ in their approach. Two states that border each other can, for example, have vastly different approaches to the way they handle zoning permits. That's not the case with marriage, which is on a different plane altogether. Our society cannot endure without a uniform definition of marriage, which is too deeply encoded in the nucleus of a healthy society to treat it as if it were just another public policy issue.

Despite our reluctance - despite the significance of the endeavor and the awesome task of changing the Constitution - prudence dictates this course of action. The threat to marriage is unambiguous and increasingly imminent. The overriding importance of marriage makes it crucial that we act now to amend the Constitution to make explicit what has always been understood as implicit - and define marriage as the union of one man and one woman.

This doesn't mean that the federal government should regulate every aspect of marriage. The states should continue to set their own policies regarding the age of consent, the rules of divorce and other pertinent marriage questions. But we must start with a common, bedrock understanding of what marriage is. And like it or not, it falls to us to codify that understanding.

This is a time for choosing.

The options are (1) to do nothing, thereby allowing a few activist judges to redefine marriage as they see fit, or (2) amend the Constitution to reflect the settled will of the people.

To protect marriage and preserve constitutional government, we must proceed with the democratic process of amending the Constitution.

Spalding is director of the B. Kenneth Simon Center for American Studies at The Heritage Foundation, a public policy research organization in Washington, D.C.