Gov. Sarah Palin’s opposition to legal abortion — even in cases of rape and incest — has given the issue new prominence. Passionate abortion foes are enthused. Passionate abortion-rights supporters are horrified.

But most voters probably won’t give the abortion issue decisive weight in choosing between John McCain and Barack Obama. And for good reason. Both political parties embrace unpopular, immoderately absolutist positions on the issue, although McCain has flirted with moderation in the past.

And even though one or more of the five Supreme Court justices who clearly support abortion rights may well retire in the next four years, neither party is likely to succeed in making it a lot harder — or a lot easier — for most women to get abortions.

Polls show that a large majority of Americans reject both Palin’s uncompromising anti-abortion vision and the Republican platform’s extreme call for banning all abortions and all embryonic-stem-cell research. Most also oppose overruling Roe v. Wade.

But most voters don’t agree with Obama’s absolutist abortion-rights record, either. Obama would make it easier for women to get abortions; most voters would make it harder. Obama would require the federal government to fund abortions for poor women; most voters oppose that. And Obama’s record as an Illinois state senator can be read as suggesting that he may have a more sweeping vision of abortion rights than any of his current Senate colleagues have.

Would a McCain-Palin victory spell doom for Roe v. Wade and constitutional protection of abortion rights? It’s an outside possibility, but I’d bet a lot against it.

I suspect that even McCain himself might not want Roe overruled, notwithstanding his repeated assurances to anti-abortion conservatives that he does. Indeed, in a revealing 1999 newspaper interview, McCain said: "Certainly in the short term, or even the long term, I would not support repeal of Roe v. Wade, which would then force X number of women in America to [undergo] illegal and dangerous operations."

McCain has since repudiated that statement. He has also courted the Religious Right not only by choosing Palin but also by vowing to choose justices in the mold of Bush-appointed Chief Justice John Roberts and Justice Samuel Alito and by giving anti-abortion absolutists a free hand with the Republican platform.

But if McCain is elected, he would not be taking his marching orders on abortion from Palin or the platform. He still supports abortion rights in cases of rape or incest. He voted last year to fund some embryonic-stem-cell research. He is well aware that a decision overruling Roe would be hugely unpopular, hurting Republican candidates at all levels for years. And in any event, McCain could get Roe overturned only if an improbable chain of events were to unfold.

First, it is unclear whether Roberts and Alito, although undoubtedly conservative, will ever join the campaign by Justices Antonin Scalia and Clarence Thomas to overrule Roe. Second, it’s very doubtful that McCain could get a Democratic Senate to confirm any nominee who is likely to overrule Roe. Third, McCain — who is far more focused on foreign threats — seems unlikely to invest much political capital in battling for such a nominee.

To put this in perspective, it seems to me less likely that Roe will be overruled in the next 10 years than it is that terrorists will detonate a nuclear bomb in Manhattan or Washington. (See Jeffrey Goldberg’s chilling analysis of that danger in a September 9 New York Times op-ed.) Choosing the candidate most likely to prevent such a catastrophe is far, far more important than choosing the one whose position on abortion seems preferable.

Even if the Court were to overrule Roe, that would not make abortion illegal. It would merely give states the option of banning or severely restricting abortion. Most would not do so. And women in anti-abortion states would remain free to get abortions elsewhere.

Roe has been on the books for 35 years. The Court has repeatedly reaffirmed its "essential holding." The public is not clamoring for change. 

This is not to deny that new restrictions could have a heartrending impact on women and girls who are desperate to have abortions but unable to cope with legal hurdles. The same is true of any restriction, however, including the current laws against infanticide-like abortions of viable, 8-month-old fetuses. Unless we are to treat all unborn fetuses as insignificant clumps of tissue, the law must draw lines.

Obama’s record suggests that he would draw those lines far to the left of center of mainstream public opinion. He said in July 2007 that "the first thing I’d do as president is sign the Freedom of Choice Act." That 19-year-old proposal, which has never passed Congress, would nullify the popular law against federal funding of abortions; end the even more popular federal ban on "partial-birth" abortion; and sweep away the broadly popular state laws requiring parental notification or consent (or judicial approval) before a minor can obtain an abortion and 24-hour waiting periods before any woman can obtain one.

Beyond that, as an Illinois legislator, Obama led the way in killing a 2003 Illinois bill nearly identical to the federal Born-Alive Infant Protection Act of 2002, which passed the U.S. Senate by 98-0. Both laws require that aborted fetuses that are alive — even if they are too premature to be "viable" (capable of surviving more than a few hours) — be given appropriate medical care and treated as full persons under the law. This has opened Obama to criticism by the National Right to Life Committee that his position was so extreme that he considered "a breathing, squirming, fully born pre-viable human baby [as] still covered by Roe v. Wade."

Obama has accused the NRLC of "lying" about his position. And he and his campaign have provided various rebuttals, including a claim that he would have supported the federal bill, and opposed the Illinois bill only because it lacked a provision specifying that abortion rights would not be affected. But the NRLC has produced documents showing that the state bill that Obama opposed in 2003 did contain such a provision, and that he knew it.

Obama has sought to sound more moderate on abortion this year, especially since he locked up the nomination. He drew criticism from abortion-rights activists and arguably departed from current law by saying in July that "mental distress" — which he later amended to merely "feeling blue" — should not be a legal justification for aborting a viable fetus.

What does the public want? It is ambivalent. Polls show that most respondents, by ratios that are sometimes close to or above 2-to-1, do not want to see Roe v. Wade overruled. But paradoxically, majorities do support some restrictions (such as spousal-notification requirements) that are barred by current law, which is already more restrictive than the original Roe; decisions over the past two decades have somewhat narrowed Roe‘s protections while preserving its "essential holding."

Indeed, a majority of adults told Gallup pollsters in May that abortion should be either illegal or "legal only in a few circumstances." A majority told a CBS News poll in October 2007 that abortion should be either banned entirely (4 percent) or permitted only to save the woman’s life (16 percent) or in cases of rape or incest (34 percent).

Such polls can be read as showing that most Americans oppose most of the abortions allowed by current law. But majorities in some other polls say that abortion should be legal in all or "most" cases. And only 31 percent told Gallup in January that abortion laws should be made "more strict," while 42 percent chose "remain as they are" and 21 percent chose "less strict." As for whether they would "only vote for a candidate who shares your views on abortion," only 13 percent of all adults (in May 2008) said yes.

I lean to the abortion-rights side of the policy debate, with increasing misgivings as the developing fetus looks less like a clump of cells and more like a baby. As a matter of constitutional interpretation, however, I agree with the many scholars who saw it in 1973 as a profoundly unwise, undemocratic, and disruptive usurpation of legislative power for the Court to strike down the abortion laws of all 50 dates and create overnight an abortion right far broader than any other nation recognizes.

But Roe has been on the books for 35 years. The Court has repeatedly reaffirmed its "essential holding." Scores of millions of women see legal abortion as their birthright. The public is not clamoring for change. Given all of this, it would be a radical and destabilizing move to overrule Roe now. I hope that Roberts, Alito, and any McCain nominees understand that.

It would also be a bad idea for Congress to flout public opinion by sweeping away with a party-line vote virtually all of the modest restrictions on abortion rights that the justices have upheld since Roe. I hope that many Democrats, including Obama, understand that, too.

CORRECTION: The original version of this column misstated Obama’s role opposing the 2003 Illinois bill.