In what is being billed as the most important firearms ruling in a generation, the US supreme court begins hearing a case tomorrow that will decide whether Americans have a personal right to own guns.

The city of Washington DC has outlawed gun possession for more than 30 years, but a 65-year-old security guard is challenging the rule which he says prevents him from keeping a gun at home to protect his family. If the supreme court strikes down the city's ban, considered the nation's strictest gun law, the floodgates could open for legal tests on rules limiting gun ownership in the US.

Bankrolling the court challenge is Robert Levy, an affluent lawyer, who believes the Washington ban violates the gun rights set out in the second amendment of the US constitution.

Regardless of which side the court supports, both the gun rights and gun control movements are bracing for a political upheaval. "It is a potentially huge, landmark decision, maybe the only decision in our lifetime in which the supreme court will tell us what the original meaning of the constitution is without being impeded by precedents," said Randy Barnett, a Georgetown University law professor.

The US gun rights movement has grown increasingly powerful despite the number of shootings in schools, including the Columbine massacre nine years ago and the murders at Virginia Tech University.

The death toll in the US from firearms far outranks other western countries. About four of every 100,000 Americans were killed by guns in 2002, compared with just 0.15 in England and Wales, according to the UK-based Gun Control Network.

It is against this politically and socially incendiary backdrop that the high court will begin examining gun possession for the first time in more than 70 years.

Lawyers for the city are conscious of the recent string of massacres in the US. They argue that the handgun ban is reasonable in the light of the danger posed by a high crime rate. "Preventing [serious] harm is not just a legitimate goal; it is a governmental duty of the highest order," the city's legal team wrote to the high court.

But Dick Heller, the security guard bringing the lawsuit, cites the local crime rate as a justification for keeping a gun at home. "I want to be able to defend myself and my wife from violent criminals, and the constitution says I have a right to do that by keeping a gun in my home," he said when the supreme court agreed to hear the case in November. "The police can't be everywhere, and they can't protect everyone all the time."

Other critics of the Washington ban view outbreaks of violence in the US as proof that gun control laws have failed.

"If you look at crime rates, [Washington] DC's crime rate skyrocketed after the ban was put in place," said Andrew Arulanandam, spokesman for the National Rifle Association. "We believe it's for the simple reason that law-abiding people didn't have the means of defending themselves."

Barnett, of Georgetown law school, pointed out that Virginia Tech advertised its broad ban on gun use before the massacre there. "Even in Britain, I don't think people would want to put a sign on their door saying, 'This is a gun free zone'," he said. "That's what Virginia Tech was."

Levy agreed: "If you could prove that gun laws are making us safer, the remedy is to change the constitution."

The outcome of the court's decision, expected in June, is likely to have an impact on the presidential election. The Republican nominee, John McCain, has joined a majority of the US Congress in opposing the Washington ban over the objections of the Bush administration, which fears that overturning the law could threaten other national gun restrictions. McCain might use the ruling to shore up his conservative credentials, particularly with voters who applauded the supreme court's shift to the right under George Bush.

But the Democrats Hillary Clinton and Barack Obama have quietly supported the city's position. A ruling that supports individual gun rights would force both to address gun control, an issue their party has played down in recent years as rightwing activists have fuelled the strength of the gun rights movement.

Legal experts say backers of gun rights could have more to lose than to gain from the court case, because the US political dynamic already favours gun owners.

"I thought this litigation was a terrible idea from the beginning, and I speak as someone who thinks the constitution guarantees an individual right [to own guns]," said Brannon Denning, a law professor at Samford University in Alabama. "Gun rights were being protected pretty well already, at least in line with what popular opinion thinks the second amendment does."

The president of The Brady Campaign to Prevent Gun Violence, a lobbying group, also predicted that the court ruling would be "a shot in the arm" for his camp.

"The only thing that hurts our efforts is if it's an extreme decision that says you can't have any limits, any time, anywhere," Paul Helmke said. "But anything short of that - that basically allows reasonable restrictions ... I think could help the gun control movement."

Quest falls to a security guard

Robert Levy, below, is so committed to defeating the strongest gun ban in America that he used his personal fortune to take the case all the way to the supreme court. But he does not even own a gun.

A senior fellow in constitutional studies at the Cato Institute, a Washington research foundation, Levy says his challenge is not about weapons or about the laws banning them, but about respect for the US constitution.

The wealthy libertarian, who graduated from law school in his 50s after making money from stock market analysis, began his quest to test the strength of gun rights with a simple recruitment drive: he needed people with compelling personal reasons for owning a gun, who would sue the city of Washington.

The dream team was found without even placing an advertisement. He chose six plaintiffs with diverse backgrounds to file lawsuits against the city handgun ban. But of the six, five had their cases dismissed by judges who did not believe they could demonstrate injury. The last man standing is Dick Heller, a security guard, who sees his case go to trial this week.