For an American crisis, an American solution: the lawsuit.

Catholic dioceses in the US are already facing a potentially crushing burden of litigation over allegations of sexual abuse by clergy. But now, as the Vatican raises its profile in the crisis, it is also emerging as a target not just for public anger - but for lawsuits.

Victims' groups and their lawyers are increasingly accusing the Vatican of bearing ultimate responsibility for what they allege to be not just an epidemic of abuse, but a conspiracy to cover it up.

Last week a Missouri man brought a suit against the Vatican under US racketeering law, claiming that the Holy See, a former bishop and four dioceses hid the transgressions of a "web of predator priests" whose sexual misconduct spans at least three decades.

The Vatican was named, according to the plaintiff's lawyer, because it required each diocese to keep secret files about problem priests whose misconduct might expose the church to scandals and lawsuits. Racketeering law is aimed mostly at organised crime, but it also includes provisions for civil cases when someone is harmed by a "pattern" of illegal activity.

Some experts say such suits may be hard to win as the Vatican will claim sovereign immunity from lawsuits.

Bringing suits lower down the church hierarchy is not so difficult, though by no means easy. easy. Plaintiffs' lawyers estimate American dioceses have already paid nearly $1bn in damages in sex abuse cases over the past 20 years - and that was at a time when the public climate for bringing such suits was far more difficult.

Now, with senior clerics widely believed to have engaged in a cover-up, juries may be more kindly disposed to alleged victims.

Still, winning such suits remains problematical because they are often not brought until the statute of limitations has run out.

Some states are considering changing their laws to eliminate the statute of limitations in civil suits alleging sexual abuse, but none has done so yet.

Plaintiffs must also defeat the defence used by some dioceses, that the First Amendment to the US constitution, which mandates separation of church and states, means such suits amount to government interference with religion.

That defence was last month rejected by the Florida Supreme Court, which ruled that Florida's constitution did not protect churches from suit. But other states have not yet followed Florida's lead.

The burden of litigation could weigh heavily on the church nonetheless, since many cases are settled before trial and others will succeed in court.

US Catholic dioceses could face exposure of as much as $1bn, legal experts say, though they caution that it may be far too early to estimate exposure with the crisis still brewing and the state of the law in flux.