Washington - John McCain did not mince words in his reaction to an important Supreme Court decision in June on the rights of suspected terrorists imprisoned at Guantanamo Bay, Cuba.

McCain called the 5-4 the ruling "one of the worst decisions in the history of this country," adding that it would result in the courts being flooded by a wave of frivolous challenges.

In the ruling, the nine-member US Supreme Court determined that Guantanamo detainees have the right to seek release in civilian courts, but the narrow margin of the decision was significant in the current presidential campaign because a single vote tipped the scale.

It was cast by justice Anthony Kennedy, often the swing moderate who often casts the deciding vote among four liberal and four conservative justices.

It is likely the next president will have the opportunity to choose at least one Supreme Court justice, likely one of the current four left-leaning justices.

This means the court could change dramatically if the Republican McCain moves into the White House. He will have a chance to add another conservative to the court, cementing a shift to the right for the long term.

It's what Republicans have long dreamed of and Democrats have long feared. An additional conservative vote could mean US abortion law could be reexamined - as activists on the religious right desire.

The constitution grants the president the power to appoint members to the Supreme Court for life. The US Senate must approve the appointment.

Many voters are concerned about the future composition of the court because it has an immense influence on US society and politics. Hardly any other high court in the world has the power that the US supreme court enjoys in this highly litigious country.

In June at the end of the 2007-08 session, the court issued decisions not only on the Guantanamo Bay detainees but also on the constitutionality of the use of lethal injection in executions, the death penalty for raping a child, the right to own a gun and the extent of damages that oil giant Exxon was ordered to pay following the Exxon-Valdez oil spill in Alaska.

Lifetime appointments mean that a seat on the supreme court opens only in case of retirement, illness or death.

The current average age of the nine justices is 68, however, among the four liberal justices the average is 75. Among them, John Paul Stevens is the oldest member of the court at 88, and Ruth Bader Ginsburg is 75 and has been treated for cancer.

The conservative justices are comparatively young, including John Roberts, 53, and Samuel Alito, 58.

If Democratic nominee Barak Obama wins the election, the court is expected to keep its current composition.

He would be expected to replace a left-liberal judge with a similar appointee. McCain, however, could complete a process initiated by President George W Bush, who nominated Roberts to carry on the conservative legacy of Chief Justice William Rehnquist and who also selected Alito to take the seat vacated by the moderate Sandra Day O'Connor after she stepped down for family reasons.

There is no doubt that the current court is more conservative than it was just a few years ago, legal experts say. But Kennedy's swing vote still gives the court a delicate balance.

McCain has already said what he envisions. His selection of conservative Alaska governor Sarah Palin as his vice presidential running mate was aimed at attracting voters from the base of the Republican party. With the same goal in mind, he has fulminated in the campaign against liberal "activist judges" and promised to nominate only judges who will strictly interpret the constitution. (dpa)