Last year, President Bush indicated he would support a constitutional amendment banning gay marriage only “if necessary.” It’s not necessary, but Bush is now set to support one. It’s dismal, divisive politics.

[IMGCAP(1)]Pretty obviously, Bush is once again pandering to his right-wing base and is trying to cause trouble for his anticipated Democratic challenger, Sen. John Kerry (Mass.), who says that he, too, is against gay marriage but opposes measures to ban it.

We’ll have to see how complete Bush’s cave-in turns out to be. Some Republicans say he will support an amendment different from the one favored by most conservatives, who would bar civil unions as well as marriage.

Even so, Bush is ready to deface the Constitution with an amendment restricting individual rights. It’s happened once before, with Prohibition, but it stands against the grand tradition of expansion of rights — to former slaves, to women, to young people.

Bush and the Christian right claim to be defending “the sanctity of marriage.” But gay couples who want to commit themselves to each other for life are not defiling the institution. They are affirming it, along with the conservative values of fidelity, monogamy and family cohesion.

They want to bolster the institution of marriage, not undermine it — at a time when half of heterosexual marriages fail, tens of millions of children grow up in one-parent households and Bush feels called upon to mount a federal social program to strengthen marriage.

I’m inclined to agree with conservatives who say that the Massachusetts Supreme Court has overreached its authority, usurping a legislative function — and by a vote of 4-3, at that — to legalize gay marriage and declare that civil unions won’t do as a substitute.

The best way for the country to get to acceptance of gay marriage would be for state legislatures to enact civil union laws, giving gays all the legal protections of marriage, and gradually move to marriage itself — perhaps creating an institution called “civil marriage” that would allow “marriage” to remain a religious institution.

One state has leapt to this result. The Massachusetts court’s logic is sound enough: “Civil marriage” is a government institution, not a religious one. Churches remain free to accept or reject the performance of same-sex marriage. For the state to deny marriage licenses to gays is to deny them equal protection under the law.

Acting by judicial fiat, the Massachusetts court has created a national uproar and a political backlash. The GOP-dominated Ohio Legislature not only acted to bar gay marriage, but also to deny state employee benefits to unmarried couples. States will be falling all over themselves to enact constitutional amendments and “defense of marriage” laws if they don’t have them already.

Once gay couples begin getting married in Massachusetts in May, right-wing groups will pressure the conservative House leadership to move on a constitutional amendment, presumably the one sponsored by Rep. Marilyn Musgrave (R-Colo.).

Her amendment goes beyond simply declaring that marriage in the United States “shall consist only of the union of a man and woman.” It adds that “Neither this Constitution, nor the Constitution of any State, nor State or Federal law, shall be construed to require that marital status or the legal incidents thereof be conferred upon unmarried couples or groups.”

Proponents claim that the proposal would permit state legislatures — but not courts — to enact civil union laws if they choose. But opponents charge that the language “legal incidents thereof” would bar civil unions.

What makes Bush’s apparent decision to back an amendment so disappointing is that it is a departure from his previous statements — in the State of the Union address, in fact — that he would do so only if forced by the courts.

The Massachusetts decision does not force Bush’s hand. A long legal process will unfold once gays from around the country begin to marry in the Bay State and seek to have their unions validated at home.

There will be state court contests, state Supreme Court rulings and, eventually, a test of whether the federal Defense of Marriage Act trumps or is trumped by the Full Faith and Credit Clause of the Constitution.

DOMA declares that no state must recognize gay marriages legalized in another state. The Full Faith clause requires that states must recognize the validity of each others’ laws.

A ruling by the U.S. Supreme Court would be years away — probably after Bush has competed a second term (if he wins one).

Bush’s decision to back an amendment, reported in The Washington Post and not denied by the White House, almost certainly is a response to pressure from anti-gay groups such as the Family Research Council, Concerned Women of America and Focus on the Family, who have put the marriage issue at the top of their 2004 agenda.

The New York Times reported that Bush’s political guru, Karl Rove, had assured the groups during a conference call that Bush would back an amendment.

Rove has been concerned that evangelical Christian voters did not turn out in adequate numbers in 2000 to save Bush from losing the popular vote, and he is determined to make sure that they do so in 2004.

And, Kerry is vulnerable on the issue because he is from Massachusetts, where the controversy is arising, and because he voted against DOMA even though he claims to oppose gay marriage.

But there are risks for Bush. A Gallup poll last week showed that by 59 percent to 36 percent, Americans do not believe that marriages between homosexuals should be recognized by the law as valid, but also that the country is split, 47 percent to 47 percent, on a constitutional amendment.

It would serve Bush right if, by appeasing the right, he offends moderates who revere the Constitution and don’t want to see it enshrine bigotry.