According to Walter Mosley, black America can change the world. It will take a commitment to global peace and equality, a readiness for self-education and grassroots political activity - and the grocery kitty in the kitchen cupboard. And who better to lead the struggle than a people for whom struggle has become a way of life?

So he suggests in his new book of essays, What Next: A Memoir Toward World Peace. It's a slim book with big ideas. Inspired by the terrorist attacks of 11 September 2001, which Mosley watched from his Greenwich Village apartment, it's a layman's guide to international harmony - and it's placed Mosley right in the firing line of cynics.

He's better known as the bestselling mystery writer in the fedora, who Bill Clinton once said was his favourite author. Through the adventures of his trademark character Easy Rawlins, the some-time detective who prowls the postwar Los Angeles underworld with his volatile sidekick Mouse, Mosley discloses both the external and internal manifestations of racism in the US. And he does it in the grand spirit of entertainment. Zoot suits and spats, unforgettable baddies with dead eyes and white clothes, gangsters, seduction, fisticuffs and battles with lead pipes - though he never manages to lose sight of the point of it all. "I write books about black male heroes," Mosley says. "Black men can read my books without fear of being humiliated, without fear of being treated in a way that's unrealistic; they're not going to be Uncle Tom, they're not gonna be Shaft, though you might have a Mouse travelling through... I create real black male characters who are heroes in their own way."

There are eight instalments in the Easy Rawlins series, including Devil in a Blue Dress, which was made into a film starring Denzel Washington, and the most recent, a slightly clumsy collection of short stories called Six Easy Pieces. There are also the Fearless Jones and Socrates Fortlow novels; another book of political essays called Workin' on the Chain Gang: Shaking Off the Dead Hand of History, about casting off the shackles of economic slavery; and a couple of less successful attempts at science fiction. With close to 20 books under his belt spanning a career of less than 15 years, Mosley is in danger of becoming prolific.

He's sitting next to his fedora in a London hotel opposite Harvey Nichols. He's stout, dressed in black, with bulging eyes and a voice used to hearing itself. He has a tendency to seem abrupt and cordial at the same time. "African Americans," Mosley says, "are the wealthiest and most powerful and most influential group of black people in the world. We could own the US government. That's a frightening thing for a black person to say."

He muses that if he could get every African American to vote one way, constituting a quarter of the national vote, and they set up an office in the backwoods of Louisiana, then George Bush would go to that little shack in the woods and ask for their help. And it's easy to imagine, as he speaks, President Bush in the woods, getting his suit dirty, because Mosley has a knack for conviction, for making the im- possible seem within reach.

The What Next essays are impassioned

and rhetorical, and written with a certain modicum of necessary idealism. It's the politics set free from the fiction, and transferred into the earnest domain of memoir. Mosley's father, the figure that haunts much of his work, appears at the beginning of the book in his experience as a soldier in the Second World War, when he identified himself as an American for the first time as a result of being shot at by German soldiers alongside his white counterparts.

For Mosley, September 11 was a similar awakening. Black America was a part of the terrorists' enemy, just as black Americans have their own economic and political enemies on US soil. "My father was the key to understanding how to deal with what had happened in the World Trade Centre, meaning to say that black American leaders weren't standing up against America's blatant attack on civil and human rights."

But, while Leroy Mosley, on coming home from the war, decided to relocate from down-south Louisiana to Los Angeles and to take his place alongside advancing white America, Walter Mosley took it a step further: he cast his eye much wider and began to nurture a spiritual concern for the rest of the world.

"There are certain things that white institutions and structures and people are doing to black people in America that I think are awful, having to do with prisons, disease, access to power. And these are issues that people are doing stuff about, and they should be doing stuff about," Mosley says. "But we are responsible for changing this world, you know. Yes, I think black Americans could lead an international peace movement. We have a dynamic history in political movements already, such as the Black Panthers, and the Christian Leadership Conference, so I think that we know better than anybody in the world how to argue with, wrangle with and fight against the power structures for freedom. We could have an incredible impact on the political geography of America, and we're not doing it, and we should be doing it, because if we don't do anything, we actually become a part of what we've been fighting against for all these years."

Mosley, now 50, a native of Los Angeles, spent 10 years working in computers before becoming a writer. He has a degree in political science and is an avid protester and lobbyist. But there is a hint of impracticality in these new essays, which has the odd effect of deeming his suggestions at once crucial, in terms of energy, yet at the same time bordering on the ridiculous. Whereas he provided no tangible solutions to casting off the shackles in Workin' on the Chain Gang, here he ventures to offer functional pointers on changing the world. He recommends decentralising the US government by sending "the Senate to Montana, the House of Representatives to Miami... and other federal courts to Mississippi or Iowa", and funding a world peace movement with the pennies in the "jelly jar".

"There are a lot of us who have a lot of disposable cash," he says emphatically, "hundreds of billions of dollars, as a matter of fact. It's possible for us to use that money in order to make a difference in the United States and in the world." That's an easy thing to say across the road from Harvey Nichols, or from a pad in Greenwich Village, but what about the black Americans without the disposable cash? And why should a history of slavery and oppression necessarily lead to the assumption that they will be willing leaders in a global march?

Mosley admits that he has written an idealistic text. But he strongly rejects any accusation of utopianism. Grassroots political activity, he agrees, does not work without a touch of idealism, and What Next, with its inflated language and urgent bombast, is nothing if not proactive. "I didn't really set out to give practical solutions," he says. "A lot of African Americans are struggling to make it every day, and I'm not gonna ask somebody to give money who doesn't have it. But the talk of money is more of a metaphor. What I'm saying is that it's the money in our pockets that's gonna change the world, you know. I see myself as one small piece in a much larger mosaic that's coming into being. And, also, there's this notion: if I don't write it, if I don't say it, then who's gonna say it?"

And Mosley himself is nothing if not bold. In publishing his thoughts, at risk of seeming ridiculous, he's working against the sense of complacency and scepticism, or more recently defencelessness, that may have stopped black people from exercising the kind of power demonstrated during the civil rights movement. One of the more feasible suggestions in What Next is the setting up of local news groups enabling people to gather for themselves an accurate picture of the world, away from media bias. On a very basic level, Mosley affirms the importance of thinking and acting for ourselves, and making our own political judgements.

"Education - learning somebody else's notion of history, somebody else's version of the universe - is not necessarily a good thing, and it certainly doesn't make you into a good person. It doesn't give you dignity. My father, he taught me to know what's right, to really know what's right in that sense where you understand it from a human point of view; like, it's wrong for a child to die. You don't need an education to know something like that."

Mosley speaks of his father, who died of cancer 10 years ago, with affection and an air of youthfulness (his mother, a Jewish Pole, is still alive; she's 83 years old and drives to work every day at the board of education where she has worked for 53 years). He cites his father as his main literary inspiration, before comics, before, among others, Langston Hughes, Albert Camus and Alice Walker's The Color Purple, the book that got his back up for its humiliation of black men, and from which began his fostering of the black male hero in contemporary literature. "My father was a great storyteller, and he loved me telling stories. And that's always stayed with me," says Mosley, who, to an extent, is living the life his father wanted to live - for Leroy Mosley also wanted to be a writer. Instead, as Mosley puts it in What Next: "He graduated from the school of hard knocks and passed me his notes."

Leroy Mosley found himself an orphan at the age of eight and grew up in abject poverty in Louisiana. His struggle was different to that of his son; he had more basic concerns, such as getting a square meal or not, getting the job or not. "All the time I was trying to be a writer my father was telling me I shouldn't do it, you know; he was worried I wasn't gonna have any money, and I think he was surprised when I became successful. A younger generation always lives a different life in this world to the generation before, and it's not so much carrying on traditions, it's learning how capitalism has further changed the life."

And how would Mosley senior have reacted to September 11? Mosley tilts his head and remarks: "What an interesting thing." He thinks about it for a while, then says: "I think my father would have felt like I do. He'd say that something has to be done."

'What Next: A Memoir Toward World Peace' is published by Serpent's Tail on Thursday (£5.99)