It was Martin Luther King Day last month and this year, as every year, the great civil rights leader was all over the TV and the papers, especially, of course, in the US.

It struck me (watching the CNN coverage particularly) that the content never varies. The footage has become familiar. Snarling dogs set on demonstrators in Birmingham, Alabama, in 1963. The "I have a dream" speech in Washington the same year. The Selma march for voter registration in 1965. The scene on the motel balcony in Memphis in January 1968, with King dying, a distraught man on one knee beside him with arm outstretched, pointing, it might be, to the place the shot came from, others frozen in horrified bewilderment.

There was nothing at all on CNN or in the New York Times, or anywhere else that I looked, from the period between the Selma march and the balcony scene. Nothing about King's political activities in the last three years of his life. Yet this was the time of his most intense activism, the only period in his life when he involved himself full-time in politics to the exclusion of all else. Why so?, I wondered.

He was a hugely famous figure at this time, and more controversial than ever before. Virtually all of his speeches and campaigning activity were covered by the press and TV. Dozens of hours of film of him in action must be stored in the archives of the major news organisations.

But it wasn't shown this year, nor last year that I can recall. It's as if the man took a three-year sabbatical after Selma, from which he emerged to visit Memphis, and was killed.

It's rare to find mention - I found none last month - of the reason he'd travelled to Memphis.

This strange circumstance becomes slightly less strange when we bring to mind that Martin Luther King's life in the 1960s fits relatively easily into an account with which the US ruling class can live comfortably, as long as the last three years are left out. Brave Baptist pastor, brilliant orator, leader of downtrodden people in moral crusade for civil rights, assassinated even as his dream comes true, revered now across a reconciled nation... Even as repellent a pair as Bill Clinton and George Bush can cheerfully sign up to all that. At no point in the story does King emerge as a challenging figure to the consensus of the day.

Throughout the first half of the Sixties, King was a popular personality with the mainstream media, never, other than in overtly right-wing and racist outlets, cast as an extremist or outright troublemaker. As he was to acknowledge himself, the networks and the major newspapers were squarely on his side as he led demonstrators into confrontation with the institutionalised racism of the southern States. TV and still-picture coverage of sweaty cops and savage dogs ripping into peaceful protesters shocked and shamed most people in the US.

Hardly anybody except the racists on the spot directly confronted him as he led voter drives or sit-ins for the right to eat at public lunch counters. Of course, the racists on the spot were not few in number. They amounted to a majority in half a dozen States and had substantial support in a score of others. They had a swathe of cops and politicians across the South on their side. Murder and rape were among their weapons. But they were not a majority in the US, and far from a majority among the real rulers of the country.

That's not to say the rulers would have conceded civil rights if they hadn't been pushed. But when pushed, they were able to give way with middling good grace, knowing that their power wasn't fundamentally threatened. The Civil Rights Acts of 1964 and 1965 were the result.

But after the passage of the acts, King didn't go away. On the contrary, he moved on to mount a sharper and much more radical challenge to the system. He noted that the equal rights formally conceded would mean little while people remained unequal in their lives generally. If you are too poor to eat in a restaurant or live in a particular neighbourhood, it signifies nothing that the law says you can.

King's major break from the ideology of his earlier days was exemplified in his increasingly frequent and specific references to class. He pointed out that most of the Americans living in poverty were white. He called for "radical changes in the structure of our society to redistribute wealth and power".

Relating these themes to the other major radical campaign of the period, King became by 1967 by far the most influential opponent of the Vietnam War in the country, declaiming that it was the blacks and the poor whites who were doing the dying, and for a cause in which they had no stake. In his "Beyond Vietnam" speech at New York's Riverside Church on April 4, 1967 - a year to the day before he was murdered - he juxtaposed the war to the Panther-led uprisings in the ghettoes - a development which ran counter to the strategy of peaceful direct action of which he had been the most passionate advocate earlier in the decade: "I cannot ever again raise my voice against the violence of the oppressed in the ghettoes without having first spoken clearly against the greatest purveyor of violence in the world today - my own government. [Blacks are dying] in extraordinary proportions relative to the rest of the population... to guarantee liberties in south east Asia which they had not found in south west Georgia and east Harlem".

Extending his economic critique to US foreign policy generally, he referred to "capitalists of the West investing huge sums of money in Asia, Africa and South America, only to take the profits out with no concern for the social betterment of the countries."

According to Jonathan Neale in his brilliant book published last year, The American War (which, incidentally, is what it is called in Vietnam) the speech "had a shattering effect on the generals".

The left-wing US commentator Danny Cassidy observes: "You haven't heard the 'Beyond Vietnam' speech on network news retrospectives, but national media heard it loud and clear back in 1967 - and loudly denounced it. Time magazine called it 'demagogic slander that sounded like a script for Radio Hanoi.' The Washington Post patronized that 'King has diminished his usefulness to his cause, his country, his people.'"

It's that view of King which cannot be incorporated into the soft-focus anniversary obits.

In 1968, in the last months of his life, King threw himself into mobilising "The Poor People's Campaign", proposing to deploy the spirit and direct-action strategy of the civil rights movement in class struggle. He wanted to bring together "a multiracial army of the poor" that would "descend on Washington". It was the most radical project of his life.

He went to Memphis in April to speak in support of the city's striking refuse workers and to urge them to enmesh their particular struggle into The Poor People's Campaign.

MLK Day, and the annual ritual celebration of a version of the man's life which goes with it, is an exercise in censorship and misrepresentation, the misrepresentation arising from the fact that the class-based system we live under can subsume any set of ideas into itself other than ideas based on the necessity of class struggle.