First, the good news, which deserves to be savoured for a moment. The inauguration in the Hague tomorrow of the first chief prosecutor of the International Criminal Court marks a remarkable moment in history. Dictators and tyrants around the world can be brought to book, by a single court. It is an astonishing achievement - and one that seemed, until just a few years ago, quite unimaginable.

Even after the signing in 1998 of the Rome Treaty, which laid the foundations for the new court, many believed that the ICC would never become real. They were wrong. Last year, the number of countries ratifying the treaty reached 60, thus allowing the court itself to be created.

The prosecutor and judges have been selected. Now, to crown that process, the inauguration tomorrow of Luis Moreno Ocampo - a former prosecutor of the Argentine junta - means that the ICC show is well and truly on the road. Last July, when the court was constituted as a formal entity, it remained without practical power. From tomorrow, its power will be tangible. The court will be authorised to prosecute some of the horrific crimes now being committed around the world - for example, in the Democratic Republic of Congo, which may provide the first cases.

Ninety countries, including almost all the world's major democracies, have now ratified the treaty. But not the United States - which is where the problems begin. Those problems are increasing by the month and by the day. The US administration, not content with refusing to ratify, and then 'unsigning' the treaty (a murky legal concept, at best), seeks to prevent this crucial instrument of international justice from building up the strength it needs to do its work successfully. It is, in short, doing its level best to kill the court. (The 'Hague invasion clause', signed into law by President Bush last year, allows him to use 'all means necessary and appropriate' to free US servicemen detained by the ICC.)

In recent days, there have been small glimmers of light. A vote in the Security Council last Thursday was 12-0 in favour of a renewal of a special one-year deal that was agreed last July, allowing US peacekeepers immunity from prosecution. That sounds like another victory for the US hawks. But equally significant were the diplomatic dogs that refused to bark: France and Germany both withheld their vote, because they were so unhappy at the US pressures. Nor was this just the same old post-Iraq rift. Kofi Annan himself warned that the court - and the Security Council - would be undermined, if such renewals became an annual routine. Many countries - from Switzerland to South Africa - spoke out against the idea that the Security Council should start rewriting international treaties.

The US pressures at the United Nations have been only part of the story. The bully tactics against countries which defy America by refusing to weaken their commitment to the court have become blatant in recent months, as private (and much-denied) arm-twisting has given way to public threats. Countries vulnerable to American pressure - these days, the list of such countries is long - are told that unless they offer the Americans the desired immunity from prosecution, punishment will be swift and severe. Thus, the US ambassador to Zagreb recently published an open letter warning that Croatia would lose $19 million in military assistance if it failed to sign. Other countries have received similar threats; some - like the Bosnians, who, one might think, had already suffered more than their fair share of threats and ultimatums in recent years - have reluctantly surrendered.

The irony is obvious: that Washington simultaneously demands complete co-operation with international justice at the Yugoslav war crimes tribunal (or else), and complete non-co-operation with international justice at the ICC (or else). Elsewhere, Caribbean countries have been told that they will no longer be eligible for hurricane assistance unless they give the Americans what they want, right now. Like every practised bully, Washington has given an early date for the implementation of its threats. For many countries, the proclaimed deadline for kowtowing to the US pressures runs out on 1 July, the first anniversary of the court itself.

The American view of the court, described by the deputy US ambassador to the UN as 'a fatally flawed institution', is that the court will act as a giant conspiracy against America. Accordingly, Americans will be unfairly targeted. But this misunderstands the essence of the court. The ICC is a court of last resort, which prosecutes only the most serious war crimes and crimes against humanity, and comes into play only where domestic courts have shown themselves unwilling or unable to prosecute. Despite the depressing and dangerous insouciance about international law shown by America at Guantanamo and elsewhere, one would assume that US politicians and commanders are not eager to commit atrocities on a grand scale, à la Saddam or Milosevic, which could bring them before the ICC.

As Kofi Annan pointed out, no UN peacekeeper of any nationality has been accused of a crime 'anywhere near the crimes that fall under the jurisdiction of the ICC'. The Americans may be right to fear that there will be attempts to bring politically motivated cases. But the court has a solid panoply of safeguards, which make it difficult to imagine that malicious and frivolous cases could get past judicial first base.

Britain, which played a key role during the negotiations of the Rome treaty five years ago, has in recent months played a less dignified role - constantly eager to tweak the European diplomatic language in order (unsuccessfully) to appease the US loathing of the court. The UK has been depressingly reluctant to confront Washington's bully tactics, confining itself instead to occasional hand wringing expressions of regret. And yet, almost no issue can be of greater importance. The strength of the ICC -which does not have retrospective jurisdiction beyond July 2002 - can become an international guarantor of stability in the years to come.

American contempt for the court - and its determination to bring the court's supporters to heel - sends a disastrous message worldwide. It suggests that there is one standard of justice for Americans and another for everybody else. Such haughty foolishness makes the world a less safe place - for Americans too.