Why are the two major presidential candidates virtually ignoring the importance of this election in determining the composition of the Supreme Court and the future of constitutional law?

One of a president's most long-lasting legacies is in the judges he places on the bench. Justice John Paul Stevens, now 88, was appointed by President Ford in 1975. If John G. Roberts Jr. remains on the court until he is 88, he would be chief justice until 2043.

Although the candidates' mentions of the issue have been few, it is clear that there is a sharp difference between them as to what type of individuals they would name to the Supreme Court. John McCain has said that he would appoint individuals like Roberts and Samuel A. Alito Jr., and that he admires the judicial philosophies of Antonin Scalia and Clarence Thomas. Barack Obama voted against the confirmation of Roberts and Alito and has said that he would appoint justices like Ruth Bader Ginsburg and Stephen G. Breyer.

The issue of judicial appointments is particularly important in this election, because there are almost sure to be vacancies on the Supreme Court during the next presidential term. It seems unlikely that Stevens will remain on the court until 2013, when he would be 93. Ginsburg is 75, and there is speculation that she might retire. It also has been widely rumored that David H. Souter wants to retire and go home to New Hampshire.

If McCain gets to replace any of these justices, let alone more than one, there likely would be dramatic changes in many areas of constitutional law. There are almost certainly four votes on the current court — Roberts, Scalia, Thomas and Alito — to overrule Roe v. Wade and allow the government to prohibit abortion.

In light of McCain's emphatic opposition to abortion rights, he likely would appoint the decisive fifth vote to end constitutional protection of those rights. Obama, by contrast, would almost certainly appoint individuals who would reaffirm Roe.

The disagreements between McCain and Obama about issues of constitutional law extend far beyond just abortion rights. McCain said that the Supreme Court's decision in June protecting the right of those held as prisoners at Guantanamo Bay to have access to federal court hearings was one of the worst in history. Obama praised it for upholding the rule of law and ensuring compliance with the Constitution. Because it was a 5-4 decision that included Stevens, Souter and Ginsburg in the majority, McCain's replacing even one of these justices could cause the court to reverse itself.

Likewise, a McCain appointment to the high court probably would cast the fifth vote to overrule the court's 2003 decision to allow colleges and universities to consider race in admissions to achieve diversity.

The presidential candidates likely have made a political calculation to avoid discussion of judicial picks, because the issue is not paramount to the all-important undecided, swing voters.

Moreover, the candidates — especially Obama — seem to want to avoid the underlying constitutional issues.

For example, Obama rarely emphasizes his support for abortion rights, being content to say that the goal should be to decrease the number of abortions. Nor does he see political gain in defending affirmative action or the rights of suspected terrorists.

But this strategy may be a serious miscalculation in what is likely to be a very close election. Each candidate needs to turn out his base of support, which does care about this crucial issue. Equally important, there may be appeal to key groups of undecided voters, such as Republican women, Hispanics and younger voters.

Even with the economic crisis and the war in Iraq as dominant political issues, there is time to discuss the president's role in filling judicial vacancies.

The stakes are no less than the content of constitutional rights for a generation to come.

Erwin Chemerinsky is dean of the school of law and a professor at the University of California, Irvine. He wrote this commentary for the Los Angeles Times.