John Paul Stevens still plays tennis at 88. Ruth Bader Ginsburg, 75, works out regularly in the Supreme Court gym.

The oldest two justices — half the court's liberal wing — top the list of those considered likely to retire during the next presidential administration. Despite Stevens' and Ginsburg's apparent vigor, change on the Supreme Court is more likely than not over the next four years.

"One would think that over the course of the next four years the actuarial tables would catch up with the oldest members, as they do for us all," said Pepperdine University law professor Douglas Kmiec.

With five justices 70 or older by the time the court meets again in October, interest groups and commentators have been talking about the court's role in the presidential election. One change on a court that divides 5-4 in key cases can alter the results.

But their forecasts depend on three factors: Who wins the presidency, who leaves the court and who is appointed.

Democrat Barack Obama would most likely be replacing liberal justices with like-minded successors. Republican John McCain could get the chance to fulfill a campaign pledge and put a conservative justice on the court in the mold of Chief Justice John Roberts or Justice Samuel Alito.

Alito, among President George W. Bush's two selections, repeatedly has demonstrated the difference one justice can make on a closely divided court. The result in disputes over abortion, religion and school desegregation almost certainly would have been different had Sandra Day O'Connor not retired in 2006.

"Given the likely retirements, the next election probably will determine whether the court gets more conservative or stays ideologically the same," said Erwin Chemerinsky, dean of the law school at University of California, Irvine.

The Supreme Court rarely becomes a big issue in the presidential campaign and this year — with $4-a-gallon gas, steep declines in the stock market and two wars — appears to be no exception.

The one case decided recently that could have elevated the court's importance in the campaign came out in favor of Americans' gun rights, placating the highly energized and politically effective gun rights groups.

If the case "had come out the other way, we'd be having a very different conversation," Thomas Goldstein, a Supreme Court watcher and advocate, told a Federalist Society meeting a week after the guns decision.

The unpredictably of Supreme Court retirements is another reason why the court rarely becomes an issue in presidential campaigns.

What if the justices decide to grow even older together?

It has happened before. Nine of the last 10 justices who retired or died in office were at least 75; six of those were 79 or older.

No one left the court during President Carter's four years in office, President Clinton's second term or Bush's first.

On the other hand, six justices ranging in age from 76 to 85 stepped down between 1986 and 1994, spanning three presidencies.

Bush had two appointments in the space of three months in 2005. He filled them with two men in their 50s, Roberts and Alito.

Goldstein predicts only Stevens will retire during the next four years and not before he surpasses Oliver Wendell Holmes — who stepped down two months shy of his 91st birthday, in 1932 — to become the oldest sitting justice. That would happen in February 2011.

Goldstein's views shifted as he watched the court over the past year. He used to expect the retirement of three justices — Stevens, Ginsburg and Justice David Souter. Though only 68, Souter has made no secret that he prefers New Hampshire to Washington and intends to return there someday.

But justices find it hard to leave the court unless they're in poor health, Goldstein said.

Chief Justice William Rehnquist didn't retire even after he was diagnosed with cancer. His death in 2005 created the second vacancy for Bush.