If George Bush is still as intent on invading Iraq as he seems to be, overthrowing the Iraqi regime and killing Saddam Hussein may well turn out to be the easy bit. The catchphrase in Washington since September 11 has been "regime change", but what regime can be put in place of the tyrant of Baghdad, who has dominated the country's politics since 1968? The task after the ousting of Saddam will be to prevent anarchy from returning to the streets of Baghdad and the oil facilities throughout the country, and the US has been looking for a strongman to put in Saddam's place.

Of course, Saddam Hussein has never had a problem with making enemies, and the breadth of the Iraqi opposition - from Islamic fundamentalists and communists to monarchists and free-marketeers - demonstrates his ability in this respect. Seemingly every week, a new group springs up and issues an identikit statement to the international media. Recently one organisation, which no-one seems to have heard of except its own members, even took over the Iraqi embassy in Germany to prove that it existed. However, there are some basic patterns to this cacophony of proclamations from new movements, councils and parties that purport to represent the voice of the authentic Iraqi individual.

Firstly, there are the national bodies that were created inside Iraq before 1990, when the bond that had formed between Iraq and the US was shattered by the invasion of Kuwait. These are groups like the Iraqi Communist Party, the largest group in Iraq from the 1950s through to the 1970s; and al-Daawa al-Islamiyya (the Islamic Call), which engineered the biggest demonstrations against the Iraqi regime in the 1970s and had close ties with Ayatollah Khomeini's Islamic revolutionaries in neighbouring Iran. With extensive experience of organisation and the political process inside Iraq, many of these group retain some level of support - or at least respect - among many of the Iraqi people. They have three things in common: they are intensely persecuted by the Iraqi regime, they are wholly unpalatable to the West, and they strongly oppose a US invasion due to the suffering this will cause the Iraqi people.

Secondly, there are the new groups, often formed under US auspices after 1990. The US has tried to encourage senior members of Iraq's military and civilian apparatuses to defect to the West, and their prize has often been a budget, some training, lavish offices, frequent meetings with US officials and the prospect of taking a leading political role in a post-Saddam Iraq. It is from these groups that the US will select the new rulers if they succeed in ousting Saddam. Some of the main contenders are:

The most senior military officer to defect since 1990, Khazraji was Saddam's chief of staff from 1980 until 1991, leading the army through the eight-year Iran-Iraq war and the invasion of Kuwait in 1990. He left Iraq in 1996, and was subsequently granted political asylum first in Spain and then in Denmark, where he now lives in a quiet suburb of Copenhagen. There are claims that he was reluctant to leave Iraq, but that the CIA tempted him with promises of a major political role after the overthrow of Saddam. As a result, he has not been quiet about his plans to lead Iraq: he once described his future leadership as a "sacred duty".

Apart from his apparent boastfulness, which has alienated many of his fellow travellers in the exiled opposition, Khazraji has more serious problems in presenting himself as a future leader of Iraq. As one of the most senior officers in the Iraqi military at the height of its repression, Khazraji was clearly involved in many of the worst abuses of the regime.

He may even have had a leading role in the single most infamous act of brutality: the chemical onslaught on the town of Halabja in March 1988. This attack killed 5000 Kurds of northern Iraq in 48 hours of intense bombardment by chemicals that cause the nervous system to collapse, the skin to burn and blister, and the lungs to flood. A Danish newspaper that investigated Khazraji's role found that he was the field commander during the Halabja operation, choosing the chemicals to be used and the intensity with which to drop them. Although Khazraji denies having had this role, the allegations were serious and detailed enough for the Danish ministry of justice to launch an official investigation, with the potential to bring war crimes charges against him. 89 different Kurdish and human rights groups have issued a joint statement to demand his trial. He has been under effective house arrest for almost a year now, guarded by four police officers.

The allegations against Khazraji do not stop there. Earlier this year, a credible eye-witness testified in video-taped evidence that he saw Kharaji entering into his village during the height of the Iraqi repression in 1988. There, according to the witness, Khazraji decided to exert his brutality upon a child. "I saw him with my own eyes how he kicked a little Kurdish child to death", said the 65-year old man.

Nevertheless, senior US officials have continued to promote Khazraji as a future leader and maintain close contacts with him. Ambassador David Mack, a senior official in the State Department who coordinates meetings of Iraqi opposition groups in Washington DC, recently said that Khazraji has "the right ingredients" and claimed that he has "a good military reputation".

A commander of an armoured division of Iraq's elite Republican Guard in the Gulf War, Salihi played a significant military role in Iraq's invasion of Kuwait. He was also engaged in putting down the uprising against Saddam Hussein's rule which followed the defeat at the hands of the US-led forces. This repressive way in which this particular episode was handled caused 1.5 million people to flee their homes. Salihi went on to write a book about the crushing of the popular uprising.

After Salihi commanded Iraqi forces in putting down another rebellion by an opposition group in 1995, he defected to the side of his former enemies and came to coordinate with the US where he now resides. In meetings at the British Foreign Office in March this year, he acquired the soubriquet of the "rapidly rising star" of the Iraqi opposition.

With the advantage of youth over many of his contenders - having just turned 50 in contrast to Khazraji's 65 - many US officials view him as the natural choice to replace Saddam. Indeed, when a popular website of Iraqi exiles held an on-line poll to find out who their preferred future leader was, Salihi raced ahead - until the poll had to be suspended amidst suspicions that it was being rigged. In any case, it wouldn't have been the first Iraqi election to produce a victor with 99.9% of the vote.

Salihi strikes a contradictory pose with regard to his future role. On the one hand, he states - to some acclaim from US commentators - that the military should not be engaged in the politics of Iraq. Then the Brigadier-General holds meetings with senior US officials, and takes part in US-sponsored seminars, to discuss the political contours of a post-Saddam Iraq.

The long-time face of the Iraqi opposition in Washington, Chalabi took the reins of the Iraqi National Congress (INC), an umbrella organisation created in 1992 with the assistance of the CIA. Although he was officially demoted in 1999 to be a simple member of the INC's executive council rather than its leader, he is widely accepted as the first among equals, and is spoken of by INC officials as the future president of Iraq.

Chalabi has managed to woo supporters from the misty fringes of the right-wing of the current US administration to left-wing campaigning UK journalists. The Times once proclaimed him as "too good to be true". He speaks elegantly of democracy, human rights and friendly relations with the US. Many of his mannerisms that appeal in the West may have been picked up from his days at a Sussex private school, where he was a member of the cadet corps - his sole training in skills he has subsequently put to use in planning an invasion of Iraq.

He came to international attention not for his politics but when he fled to London from Jordan in 1989 amidst allegations that he had embezzled millions from the bank he used to own. Although he denies any wrong-doing, the collapse of the Petra Bank left thousands of its customers without their savings and in penury, and earned him stinging comparisons with Robert Maxwell. He did not return to Jordan to defend himself at his trial in 1992, which took place in his absence. Chalabi claims that the trial was politically motivated. However, the Jordanian government was supporting the Iraqi opposition at the time, and Chalabi's trial seems to have been more a political embarrassment for them than a vendetta. He will only begin his 32 years in prison if he returns to Jordan, which he shows no sign of doing at present.

More recently, the US State Department found that about half of the $4m it had give to the INC was not properly accounted for. They clearly expected better from a former maths professor and banker, and cut off their funding for him. Chalabi managed to galvanise his American supporters, and the Pentagon and the White House started picking up the tabs for the INC.

Chalabi has one great strength that he has played repeatedly to survive: he can pull rabbits out of hats. Just as the US was forgetting him, in the wake of more accusations of his financial irregularities, he came up with a plan to unseat Saddam in a choreographed 11-week manoeuvre. The plan, to turn untrained volunteers into successful revolutionaries, provided him with the soundbite necessary to capture US policymakers' minds in the wake of September 11. Launched from Chalabi's sumptuous Mayfair home, few stopped to question if the plan verged on the unrealistic.

The son of a leading politician from the era when Iraq was ruled by British-installed kings, Chalabi has again hooked up with a royalist pretender, Sharif Ali bin al-Hussein, the cousin of the deposed king and now a London-based banker. Neither of the bankers have been to Baghdad since 1958, and have no leadership experience. That may be part of their appeal in Washington: they can take on the role as the figureheads of a post-Saddam Iraq, whilst the US can install its military strongmen behind the throne.

The CIA and US State Department, long suspicious of Chalabi, have placed many of their hopes in a different group, the Iraqi National Accord (INA). Consisting of former military officers and cronies of Saddam Hussein, it made its name by planting bombs inside Iraq. In 1994, it bombed a Baghdad cinema, newspaper offices and a mosque, killing up to 100 civilians in the process. A former INA agent has also claimed that he was ordered to bomb the headquarters of the INC by one of the leaders of the organisation. Nevertheless, it has kept up good relations with the US, and continues to receive its financial support.

A number of other groupings of former military officers have been established. In July, a conference was held in Kensington Town Hall of one of these groups, the Iraqi National Coalition. A leading light in the Coalition is General Saad Ubeidi, who once held the ominous title of the army's head of psychological operations. Although the Council disavows a future role as a ruling junta, it already stridently publicises its views on global and economic issues, so it clearly has an agenda beyond that of ousting Saddam.