The overthrow of the Shah of Iran by people's power in 1979 resounded around the world.

He was pro-western and backed by the United States.

That evoked a deep response among Arabs, who saw in Islam a focus for the humiliation they felt at the hands of the West and their disillusion with autocratic Arab nationalist regimes.

The Islamic state established by Ayatollah Khomeini stimulated the growth of political Islam in many Middle East and north African countries - in Egypt, in Jordan, in Algeria and Sudan.

The Ayatollah put survival of the Islamic State above religion

That was the case even though the Iranians are not Arabs, and their Shi'ite clerical hierarchy is at variance with the Sunni tradition dominant in the Arab world.

For the West, Iran mattered because of its oil wealth and large population: it was a big regional player.

But Western governments saw the Islamic state in Tehran as fundamentally anti-democratic, even though it held lively elections.

Liberals in Arab countries, too, voiced doubts about whether any state that claimed to be governing with the authority of the Koran could tolerate opposition.

That argument was used in Algeria to justify the army's intervention in 1992 to stop Islamic militants from taking over - even though they had won a democratic election. It was said that, once in power, they would never give it up.

Test case

Now Iran is again an emblematic test case - this time of whether a state run by political Islam can evolve peacefully towards a more pluralist system, more democratic in the Western sense.

Cleaning up after street protests

Mohammed Khatami was elected two years ago on a platform of reform and cautious liberalisation.

In the eyes of many of his supporters, he has not delivered, because the conservative clerical establishment holds the key levers of power and can sabotage his efforts - by restricting press freedom, for example.