The promised attack on Iraq will test free journalism as never before. The prevailing media orthodoxy is that the attack is only a matter of time. "The arguments may already be over," says the Observer, "Bush and Blair have made it clear . . ." The beating of war drums is so familiar that the echo of the last round of media tom-toms is still heard, together with its self-serving "vindication" for having done the dirty work of great power, yet again.

I have been a reporter in too many places where public lies have disguised the culpability for great suffering, from Indochina to southern Africa, East Timor to Iraq, merely to turn the page or switch off the news-as-sermon, and accept that journalism has to be like this - "waiting outside closed doors to be lied to", as Russell Baker of the New York Times once put it. The honourable exceptions lift the spirits. One piece by Robert Fisk will do that, regardless of his subject. An eyewitness report from Palestine by Peter Beaumont in the Observer remains in the memory, as singular truth, along with Suzanne Goldenberg's brave work for The Guardian.

The pretenders, the voices of Murdochism and especially the liberal ciphers of rampant western power can rightly say that Pravda never published a Fisk. "How do you do it?" asked a Pravda editor, touring the US with other Soviet journalists at the height of the cold war. Having read all the papers and watched the TV, they were astonished to find that all the foreign news and opinions were more or less the same. "In our country, we put people in prison, we tear out their fingernails to achieve this result? What's your secret?"

The secret is the acceptance, often unconscious, of an imperial legacy: the unspoken rule of reporting whole societies in terms of their usefulness to western "interests" and of minimising and obfuscating the culpability of "our" crimes. "What are 'we' to do?" is the unerring media cry when it is rarely asked who "we" are and what "our" true agenda is, based on a history of conquest and violence. Liberal sensibilities may be offended, even shocked by modern imperial double standards, embodied in Blair; but the invisible boundaries of how they are reported are not in dispute. The trail of blood is seldom followed; the connections are not made; "our" criminals, who kill and collude in killing large numbers of human beings at a safe distance, are not named, apart from an occasional token, like Kissinger.

A long series of criminal operations by the American secret state, identified and documented, such as the conspiracy that oversaw the "forgotten" slaughter of up to a million people in Indonesia in 1965-66, amount to more deaths of innocent people than died in the Holocaust. But this is irrelevant to present-day reporting. The tutelage of hundreds of tyrants, murderers and torturers by "our" closest ally, including the training of Islamic jihad fanatics in CIA camps in Virginia and Pakistan, is of no consequence. The harbouring in the United States of more terrorists than probably anywhere on earth, including hijackers of aircraft and boats from Cuba, controllers of El Salvadorean death squads and politicians named by the United Nations as complicit in genocide, is clearly of no interest to those standing in front of the White House and reporting, with a straight face, "America's war on terrorism".

That George Bush Sr, former head of the CIA and president, is by any measure of international law one of the modern era's greatest prima facie war criminals, and his son's illegitimate administration a product of this dynastic mafia, is unmentionable.

The rest of the answer to the incredulous question raised by the Pravda editors in America is censorship by omission. Once vital information illuminates the true aims of the "national security state", the euphemism for the mafia state, it loses media "credibility" and is consigned to the margins, or oblivion. Thus, fake debates can be carried on in the British Sunday newspapers about whether "we" should attack Iraq. The debaters, often proud liberals with an equally proud record of supporting Washington's other invasions, guard the limits.

These "debates" are framed in such a way that Iraq is neither a country nor a community of 22 million human beings, but one man, Saddam Hussein. A picture of the fiendish tyrant almost always dominates the page. ("Should we go to war against this man?" asked last Sunday's Observer). To appreciate the power of this, replace the picture with a photograph of stricken Iraqi infants, and the headline with: "Should we go to war against these children?" Propaganda then becomes truth. Any attack on Iraq will be executed, we can rest assured, in the American way, with saturation cluster bombing and depleted uranium, and the victims will be the young, the old, the vulnerable, like the 5,000 civilians who are now reliably estimated to have been bombed to death in Afghanistan. As for the murderous Saddam Hussein, former friend of Bush Sr and Thatcher, his escape route is almost certainly assured.

The column inches now devoted to Iraq, often featuring unnamed manipulators and liars of the intelligence services, almost always omit one truth. This is the truth of the American- and British-driven embargo on Iraq, now in its 13th year. Hundreds of thousands of people, mostly children, have died as a consequence of this medieval siege. The worst, most tendentious journalism has sought to denigrate the scale of this crime, even calling the death of Iraqi infants a mere "statistical construct". The facts are documented in international study after study, from the United Nations to Harvard University.

Among those now debating whether the Iraqi people should be cluster-bombed or not, incinerated or not, you are unlikely to find the names of Denis Halliday and Hans von Sponeck, who have done the most to break through the propaganda. No one knows the potential human cost better than they. As assistant secretary general of the UN, Halliday started the oil-for-food programme in Iraq. Von Sponeck was his successor. Eminent in their field of caring for other human beings, they resigned their long UN careers, calling the embargo "genocide".

Their last appearance in the press was in the Guardian last November, when they wrote: "The most recent report of the UN secretary general, in October 2001, says that the US and UK governments' blocking of $4bn of humanitarian supplies is by far the greatest constraint on the implementation of the oil-for-food programme. The report says that, in contrast, the Iraqi government's distribution of humanitarian supplies is fully satisfactory...The death of some 5-6,000 children a month is mostly due to contaminated water, lack of medicines and malnutrition. The US and UK governments' delayed clearance of equipment and materials is responsible for this tragedy, not Baghdad."

They are in no doubt that if Saddam Hussein saw advantage in deliberately denying his people humanitarian supplies, he would do so; but the UN, from the secretary general himself down, says that, while the regime could do more, it has not withheld supplies. Indeed, without Iraq's own rationing and distribution system, says the UN Food and Agriculture Organisation, there would have been famine. Halliday and von Sponeck point out that the US and Britain are able to fend off criticism of sanctions with unsubstantiated stories that the regime is "punishing" its own people. If these stories are true, they say, why does America and Britain further punish them by deliberately withholding humanitarian supplies, such as vaccines, painkillers and cancer diagnostic equipment? This wanton blocking of UN-approved shipments is rarely reported in the British press. The figure is now almost $5bn in humanitarian-related supplies. Once again, the UN executive director of the oil-for-food programme has broken diplomatic silence to express "grave concern at the unprecedented surge in volume of holds placed on contracts [by the US]".

By ignoring or suppressing these facts, together with the scale of a four-year bombing campaign by American and British aircraft (in 1999/2000, according to the Pentagon, the US flew 24,000 "combat missions" over Iraq), journalists have prepared the ground for an all-out attack on Iraq. The official premise for this - that Iraq still has weapons of mass destruction - has not been questioned. In fact, in 1998, the UN reported that Iraq had complied with 90 per cent of its inspectors' demands. That the UN inspectors were not "expelled", but pulled out after American spies were found among them in preparation for an attack on Iraq, is almost never reported. Since then, the world's most sophisticated surveillance equipment has produced no real evidence that the regime has renewed its capacity to build weapons of mass destruction. "The real goal of attacking Iraq now," says Eric Herring, "is to replace Saddam Hussein with another compliant thug."

The attempts by journalists in the US and Britain, acting as channels for American intelligence, to connect Iraq to 11 September have also failed. The "Iraq connection" with anthrax has been shown to be rubbish; the culprit is almost certainly American. The rumour that an Iraqi intelligence official met Mohammed Atta, the 11 September hijacker, in Prague was exposed by Czech police as false. Yet press "investigations" that hint, beckon, erect a straw man or two, then draw back, while giving the reader the overall impression that Iraq requires a pasting, have become a kind of currency. One reporter added his "personal view" that "the use of force is both right and sensible". Will he be there when the clusters spray their bomblets?

Those who dare speak against this propaganda are abused as apologists for the tyrant. Two years ago, on a now infamous Newsnight, the precocious apostate Peter Hain was allowed to smear Denis Halliday, a man whose integrity is internationally renowned. Although dissent has broken through recently, especially in the Guardian, to its credit, that low point in British broadcasting set the tone. If the media pages did their job, they would set aside promoting the careers of media managers and challenge the orthodoxy of reporting a fraudulent "war on terrorism"; they owe that, at least, to aspiring young journalists. I recommend a new website edited by the writer David Edwards, whose factual, inquiring analysis of the reporting of Iraq, Afghanistan and other issues has already drawn the kind of defensive spleen that shows how unused to challenge and accountability much of journalism, especially that calling itself liberal, has become.

It is time that three urgent issues became front-page news. The first is restraining Bush and his collaborator Blair from killing large numbers of people in Iraq. The second is an arms and military technology embargo applied throughout the Gulf and the Middle East; an embargo on both Iraq and Israel. The third is the ending of "our" siege of a people held hostage to cynical events over which they have no control