Against a background of campus shootings and a high murder rate, gun control activists are hoping the court will agree individual states can pass their own gun control laws.

The case was brought by a security guard, Richard Heller, who wants to overturn the law of Washington DC that bans handgun ownership.

Mr Heller argues that the Second Amendment of the constitution allows individuals to keep weapons, and that the city must follow suit.

Victory for Mr Heller could force a chain-reaction across the US as dozens of states are forced to repeal their gun laws, making the coming decision as important for gun control as Roe v Wade was for abortion rights.

"These are extreme measures," said Mr Heller's lawyer Alan Gura of Washington's handgun ban.

But Washington argues that, with firearms crime exploding across America, the city had to take action. "Handgun crime has gone down since the law was enacted," said the mayor, Adrian Fenty.

At issue is probably the most contentious sentence in the US constitution, a phrase that has been argued about for generations.

The Second Amendment states: "A well-regulated militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

America's most eminent constitutional lawyers are split on whether this limits gun ownership to members of militias, a debate fuelled by the vagueness of the original phrasing.

But no test case has managed to resolve the issue: the last time the Supreme Court tried was 70 years ago, and it failed to issue a definitive judgment.

For Washington DC, the meaning of the Second Amendment is clear. "It is related to the use of weapons as part of the civic duty of common defence," said Washington's lawyer, Walter Dellinger. 

"This (The DC law] is an extremely reasonable law. They have singled out handguns because they are mobile, they can be taken on buses, on the metro, into schools."

The judges yesterday appeared split, with some arguing that the United States had moved on since the days when settlers had to guard against bands of brigands. "We now have police departments," said Justice Stephen Breyer. "We give leeway to cities and states to work out what is reasonable."

Against this, conservatives insist that if the framers of the constitution had wanted to ban guns, they would have said so outright, as did the authors of the English Bill of Rights, on which much of the US constitution is based.

"As I remember legislation against Scottish Highlanders, legislators forbade them to bear arms," said conservative judge Antonin Scalia.

What makes the ruling so crucial is that, without a firm constitutional judgment to guide them, growing numbers of states are passing their own gun-control laws.

The court decision is expected this summer, guaranteeing that it will become a key issue in the November presidential election. 

Few debates polarise Americans like gun control, with Democrats overwhelming for it and Republicans against, and the Bush administration urging the judges to rule in favour of gun ownership. 

The last Supreme Court ruling on the topic came in 1939 in US v Miller, which involved a sawn-off shotgun.