Chile's former dictator is at the center of the debate   RELATED VIDEO CNN's Richard Blystone reports Windows Media 28K 56K

From Correspondent Richard Blystone

LONDON (CNN) -- A former military ruler under arrest in Britain, fighting extradition to Spain over crimes committed in Chile, with half a dozen more countries ready with their own lawsuits. Try looking that up in your law book.

Spanish Judge Baltazar Garzon wants to try ex-strongman Augusto Pinochet for genocide, terrorism and torture of Spaniards in Chile and Chileans now in Spain, committed during Pinochet's 17-year rule.

That itself is new. But the case before Britain's House of Lords is about more: It's about whether international law can outweigh the law of a nation.

The Nuremberg Trials were the first to prosecute international crimes

When Garzon asked Britain to extradite Pinochet, he was just the latest to push at the frontiers in the long-term evolution of international law.

The best-known landmark so far: the 1948 Nuremberg Trials of Nazi German officials for war crimes and genocide.

"The Nuremberg Trials established the principle that there are some things that are so wrong that they're wrong everywhere, and can be punished by any court," said law professor James Michael of University College London.

But those trials were imposed by the winners of a war. There was no stone tablet of universal laws to refer to. Nuremberg happened because people had the will to make it happen.

A real system of international law would need formalizing. Step by step over the last half-century, governments and international bodies have given shape to public attitudes with a succession of agreements and conventions. Some define human rights; others establish violations such as genocide and torture.

The key principle: If a state cannot or will not prosecute violations of international norms, the world has a right to.

Things have changed partly because, outraged by pictures of atrocities, the world's general public seems to be taking human rights more seriously.

"The old idea of sovereignty was, 'I have my country; you have yours. You don't interfere with my legal system or my precedent; I won't interfere with yours,'" said British barrister Michael Birnbaum. "Now, that's changing, because countries are beginning to feel it's necessary to have some kind of international system of justice."

In the Pinochet case, the British prosecution, acting for Spanish authorities, asked Britain's highest appeals court to reverse a ruling that, under British law, heads of state are immune from prosecution for crimes committed while they are in power.

Wednesday's ruling could send shockwaves around the world

The idea is that the head of one state should not be vulnerable to possibly malicious legal action by another.

That principle would shield U.S. President Bill Clinton, for example, from prosecution over the U.S. attack on Sudan in August, or former British Prime Minister Margaret Thatcher from facing trial over the Falklands War.

But prosecutors in Pinochet's case argue that international law should predominate. They claim, though it is contested, that under international law, there's no immunity for crimes against humanity.

Does Chile's "Dirty War" against real and suspected enemies of the regime -- more than 3,000 people killed -- amount to crimes against humanity?

The prosecutors maintain the kidnapping, torture and murder were indeed widespread and systematic enough to qualify.

If they win, the shockwaves will be felt not only in law courts, but in the palaces of dictators around the world.