Bilal al-Adib is a leader of al-Da'wa, the original Shi'ite underground which, over two decades and more, has paid a very high price, to no avail, in its campaign of violence against President Saddam Hussein and his hated, "apostate" regime. He was speaking in a recent interview in his office in the centre of Tehran.

"The people," he began, "will only rise up to destroy the monster when . . . " - he paused, in search, apparently, of the truly eloquent phrase; and it was with a gesture of mock despair that he finally delivered it - "only", he declared, "when they know the monster is already gone."

With this logical absurdity he captured the central dilemma of the entire Iraqi opposition, from militant Islamists like himself to the militant secularists of the communist party and the vast array of ethnic, sectarian, ideological and factional tendencies in between.

It is this opposition to which, in the wake of the latest, narrowly averted Anglo-American onslaught, the US and Britain are now turning as a means of dealing with, and eventually, it is hoped, disposing of the Iraqi dictator once and for all.

Even as he announced on Sunday that the US had, in extremis, stayed its military hand, President Clinton said that the US wanted to see a "new" and "representative" government in Baghdad. His administration would implement the recently-passed Iraqi Liberation Act, the aim of which is to bring about Saddam's overthrow in a popular uprising.

The US has long balked at such an activist strategy; but sheer despair at the absence of any alternative seems to have taken possession of it. Its chief Iraqi partner will evidently be the Iraqi National Congress (INC), a broad-based coalition set up after the Gulf war with the object of replacing Ba'athist tyranny with a truly "democratic and pluralist" new order. Its London-based leader, Mr Ahmad Chalabi, had a prominent meeting this week with the US Secretary of State for Near East Affairs, Mr Martyn Indyk.

Basically there have always been three ways that President Saddam could go.

The first, even now perhaps the most likely, is one which neither the Iraqi opposition, the US or anyone else could ever hope to play much part in bringing about. That is Saddam's assassination by one his entourage, or some other such inherently unpredictable convulsion within the obscure, treacherous, incestuous universe of his ruling house.

The second is the military coup. This, with or without Western support, has been tried again and again. But Saddam is virtually coup-proof.

He may have laid waste his country but, in terms of seizing and preserving power, he is one of the 20th century's most successful and durable despots.

The only other way is a popular uprising. That is something which, the more resources, planning and preparation go into it, the more likely it is to succeed. But three factors make it a daunting challenge all the same.

The first is that terrifying personal charisma of which the Da'wa leader spoke and which, in the final analysis, holds the whole despotic system together. Saddam's almost magical aura of invulnerability, of calm, invincible self-assurance, his proven immunity to all the shocks and disasters he has brought upon himself, his regime and his people, are such that, while everyone dreams of getting rid of him, everyone is convinced, like al-Adib, that it will forever remain a dream.

The people tried an uprising once, in the immediate, chaotic aftermath of Iraq's defeat in the Gulf War. The circumstances were highly favourable. Yet, in a horrifying bloodbath, Saddam relentlessly turned the tables on the Shi'ite south, where the rebellion had begun, and then on the Kurds of the mountainous north, who fled in mad stampede across the borders of Turkey and Iran.

Never again, the opposition and ordinary people alike proclaim: the memory is like a curse that haunts and paralyses them.

The second factor is the opposition's internal disarray. This is largely Saddam's achievement too. Inside the country the least attempt at political organisation means imprisonment, torture, execution; dissenting politics is possible only in the enfeebling remoteness of exile. In their diaspora, Saddam has managed to infect the opposition with all the contradictions of a naturally fissiparous society which he suppresses by brute force at home.

The Sunni Muslims of central Iraq, who represent perhaps 17 per cent of the population, always dominated the country's political life. But no ruler exploited their traditional ascendancy as Saddam did. This has greatly exacerbated sectarian and ethnic tensions, be it between the Sunni minority and the Shi'ites (who represent a good 60 per cent of the population), or between the Kurds and Arabs, Shi'ite as well as Sunni.

As a result, with one or two notable exceptions, the opposition itself breaks down on sectarian and ethnic lines, and what makes that even worse is that, in exile, its components gravitate towards an external sponsor congenial to them on similar grounds.

This is especially true of the Shi'ites, whose main opposition leaders are not merely heavily dependent on Iran, but imbued with its fundamentalist ideology. The most prominent of them, Ayatollah Bakr al-Hakim, head of the Supreme Council for Islamic Revolution in Iraq, hankers after some kind of "Islamic state" on the Khomeinist model.

That is as inimical to the Kurdish opposition, in their Western-protected northern enclave, as it is to the Saddam-controlled Sunnis of the centre. Kurdish leaders will not join a concerted campaign to bring down Saddam without cast-iron guarantees from others, Iraqi and Western, about their future in a federal new order; they do not have them yet.

Another great weakness of the opposition is that it boasts so few Sunnis. Kurds and Shi'ites suspect that even those few, a scattering of largely superannuated cliques, share the fear, exploited to the hilt by Saddam, that a democratic and pluralist Iraq would end their community's historic ascendancy.

The third factor that disables the opposition is its profound mistrust of Western, especially American, intentions. In 1991 the people took President Bush at his word when he called on them to rise up against the tyrant; but then, though they were still deep inside Iraqi territory at the time, American forces did nothing as Saddam, virtually under their noses, slowly, methodically reconquered his lost provinces.

So, for the opposition, it is not enough for the US merely to say that it wants to get rid of Saddam.

"We cannot forget that betrayal," Ayatollah Hakim told me early this year. "Of course our people hate Saddam, but they also hate the West for saving him and his system; perhaps they now do want Saddam out, but we think that they still want the system."

But suddenly to some, at least, of the opposition, it looks as though the US is at long last getting serious. "Saddam has done us a great service in these past three weeks," said Mr Aras Habib, a young blood of the INC, "he forced Clinton's hand."

Indeed there is little doubt that Mr Chalabi, the INC's brilliant, dynamic, if controversial, leader, is coming into his own again. His was the most serious attempt, soon after the Gulf war, to establish an all-Iraqi, multi-sectarian, multi-ethnic opposition movement. For a while, from its base in the Kurdish enclave, it actually operated out of Iraqi territory itself.

That came to an end with the Kurdish civil war which broke out in 1995; perhaps the most important single component of the INC, Mr Massoud Barzani's Kurdistan Democratic Party, turned harshly against it, and it was further depleted by other defections.

Mr Chalabi is the leading theorist and champion of a popular uprising, or some variant of it. The basic idea is that the opposition forces should converge gradually from the periphery to the centre, from Kurdish north and Shi'ite south to Saddam's natural stronghold, the Sunni centre. They should do so in a phased, incremental, co-ordinated insurgency which would encourage more and more people, freed at last from their neurosis of paralysing fear, to join it as it goes along.

With planning and gradualism it would, it is hoped, spare Iraq, the region and the world from the twin perils of any sudden, unplanned, all-out insurrection like that of 1991: another ghastly failure, or success achieved only at the price of plunging this most strategic of countries into chaos, partition and civil war, and the competing interventions of outside powers.

Western support is absolutely vital. The INC sees it as a matter of reciprocal confidence-building. The more the West gives, in real, practical terms, the more the INC will prove itself a worthy partner in return, the better able to draw other opposition parties, hitherto deeply sceptical, into the fray.

Practical support means money, training, logistics, leading to the establishment of safe havens in the already Western-protected Kurdish north and then, more critically, in the Shi'ite south. These would lie along the Kuwait and Saudi borders.

To the southern no-fly zone from which the Western powers have long since banned Saddam's war planes would be added a no-drive zone from which they would ban his armour and artillery. Saddam would then be powerless to suppress the havens, the INC says, because he knows full well that if he used the only means still available to him, infantry, the soldiers would desert to the rebel camp.

"Some disagree with us," says Mr Habib, "but I know from personal experience in the marshes that 500 properly trained, disciplined, well-led men would be enough to start with; in 24 hours they would be 1,000 - and so on till we reached Baghdad."