Ever since, while continuing to develop his liguistic theories, he has been the most prominent US critic both of his country's foreign policy and of the intellectuals and media that give it overwhelming consensual support. "The Responsibility of Intellectuals" was followed by a series of ever more devastating attacks on American policy in Vietnam (collected in American Power and the New Mandarins and At War With Asia): by 1970, he was far and away the best known intellectual opponent of the US war effort.

After the US withdrawal from Vietnam in 1975, he expanded his field of fire with a string of articles and books. All are worth reading, but several stand out. In 1979, the two volumes of The Political Economy of Human Rights, co-authored with Edward Herman, exposed America's backing for Indonesia's war against East Timor, its responsibility for the rise of Pol Pot in Cambodia and its support for bloody dictatorships in Latin America. In 1982, Towards a New Cold War subjected the US rearmament programme and its apologists to an unrelenting political attack.

Next was The Fateful Triangle (1984), an assault on US sponsorship of Israel's suppression of the Palestinians, which prompted Zionist accusations that Chomsky was a "self-hating Jew". It was followed by Turning the Tide (1985), opposing the US siege of Nicaragua and support for death squads and dictatorship in El Salvador and Guatemala. In the late 1980s and early 1990s came a further batch of writings on the media (notably Necessary Illusions), Latin America (Year 501), the Iran-Contra scandal (The Culture of Terrorism), and the cold war (Deterring Democracy). A volume on the "new world order", World Orders Old and New, is out in October (in Britain as a Pluto paperback).

Chomsky is a critic, not a policy-maker, a whistle-blower rather than a strategist furnished with alternatives. Today, he is using all his considerable powers of argument against calls for the US military to go into Bosnia and Haiti. Although he backs the lifting of the UN embargo on arms sales to Bosnia, he says: "I find it hard to take seriously those people who are saying 'Let's intervene'. It just happens that there's one country that's offered to send forces to protect Bosnia -- Iran. I haven't heard anyone agree to that, and there's a straightforward reason. If Iran were to invade Bosnia to save it from Serbian attack, the result would not be pretty. The same problems arise with anyone else."

As for Haiti, he comments: "The people there don't want US intervention. They understand what it means, from bitter experience -- the end of the grassroots movements, the end of any hope of democracy."

Chomsky has amassed an extraordinary body of evidence to show that, since 1948, the US has operated a foreign policy of refusing to allow radical nationalist third-world regimes to come between the US and the raw materials needed by its industry. Military intervention has been used consistently to this end -- and the media have given the policy almost unstinting support.

But the single-mindedness of Chomsky's critique has unnerved many commentators. Mainstream journalists get particularly hot under the collar about his "propaganda model" of the workings of the US media, according to which television networks and the press slavishly defer to the government line on every contentious foreign policy question. It's far more complex than that, say the journalists. Chomsky will have none of it. Every piece of research he and Edward Herman have conducted on media coverage of Nicaragua in the 1980s shows "a degree of conformity to power that would rarely be attained in a totalitarian state", he says. "The only time that the propaganda model is falsified is when the media turn out to be even more servile to the interests of the state than we would expect."

Still more controversially, Chomsky has been criticised, particularly from the right, for being soft on communism and third-world authoritarianism. He has always concentrated his fire on the US and has consistently argued for solidarity with the victims of US policy. Where, ask the critics, are his polemics against the Soviet Union's intervention in Afghanistan, Pol Pot's genocide, Cuba's drug-running or the PLO's terrorism?

Chomsky dismisses this line of criticism out of hand. "If you look at all of the stuff I wrote about the Vietnam war, there's not one word supporting the Vietcong," he says. "The left was all backing Ho Chi Minh: I was saying that North Vietnam is a brutal Stalinist dictatorship. But it wasn't my job to tell the Vietnamese how to run the show. My view is that solidarity means taking my country, where I have some responsibility and some influence, and compelling it to get its dirty hands out of other people's affairs. You give solidarity to the people of a country, not the authorities. You don't give solidarity to governments, you don't give it to revolutionary leaders, you don't give it to political parties.

"The point is that the people of a country should be free to do what they want -- and the main reason they're not is that we've got our boots on their necks. Once our boots are off their necks, it's up to them to figure out how to be free. If they're left with an oppressive government, then they can overthrow it -- and maybe I'll help them." Chomsky's refusal to extend support to governments and leaders is rooted in his underlying anarchist political philosophy. This world-view is based in part on the notion that a capacity for self-realisation and freedom is an unchanging part of human nature (an idea not unrelated to the central thesis of his linguistic theory that, as part of our genetic make-up, we all have an innate capacity for acquiring the rules of language). But it is also based on Chomsky's study of Spanish anarcho-syndicalism and of the dissident libertarian Marxism of 1920s and 1930s council communism -- an underground socialist tradition he first came across through friends and family as a teenager in the 1940s.

"I disagree with the orthodox left on just about everything, going back to the Bolshevik revolution," he says: all the Bolsheviks managed to create was a form of state capitalism. "That was a defeat for socialism. Lenin and Trotsky destroyed the factory councils, remade the soviets and wiped out every socialist tendency in the revolution. Leading socialist intellectuals like Anton Pannekoek and Rosa Luxemburg saw at once that it was counter-revolutionary."

Unlike the majority of anarchists, who argue that direct action is the only form that anarchist politics can take, Chomsky does not believe that his political philosophy dictates particular political tactics. "The basic anarchist idea is that any system of authority has to prove its legitimacy: if it can't prove its legitimacy then it ought to be eliminated. Occasionally a system of authority can justify itself. If it can't, and it's important enough, well, you have to undermine it. How you do so depends on the situation. There's nothing in anarchism that tells you how to proceed."

This means that, sometimes, even traditional reformist activity is the best way forward. Chomsky is a member (albeit "very passive") of Democratic Socialists of America, the Socialist International affiliate in the US that boasts a handful of supporters among Democrat Congressional representatives. "You can be anti-parliamentarian -- and indeed I am -- and still think it's important to deal with parliament," he says. "If you're trying to stop US terror in central America, it's sometimes very effective to lobby Congress. There are no new ideas in political strategy -- just constant educating and organising."