Franklin D Roosevelt was not naturally American: he was rich and a Democrat; he spoke in sentences; he sat down most of the time – a condition that has been scientifically related to "thought"; and he it was who opined that the republic he led had "nothing to fear but fear itself". In these recent months, that warning has had time to sink in.

Franklin D Roosevelt was not naturally American: he was rich and a Democrat; he spoke in sentences; he sat down most of the time – a condition that has been scientifically related to "thought"; and he it was who opined that the republic he led had "nothing to fear but fear itself". In these recent months, that warning has had time to sink in.

While 9/11 is still regarded by most Americans as an assault on New York (the American penis) and God-fearing courage, hardly a soul perceived the literal attack on trade. Oh, the cunning of the Islamic plot: to offer up to the US scenarios of constitutional outrages, cruel wars and the snuffing out of rights, when, as any American knows, the country has meagre interest and little concern for those things, but is born and raised in a foetal crouch that hovers over the thing called the economy.

And what a miracle of intimidation and mind-altering it has been that in so many Americans that essential first principle should now be forgotten. How else is it that a president is so praised and esteemed for a rapid dissolution of the economy that once would have raised cries of treason? In two-and-a-half years, surplus has become wreckage, with the ruin set on such an accelerating course that the possibility of Mr Bush being Osama bin Laden is beggingly available. What has he done but weaken the nation while ensuring the hatred of all Arabs?

Of course, God, or, if you prefer it, "God", must have a sense of irony still. After all, God more or less made America available for anyone, and endowed it with a mixture of natural resources and unflawed beauty that can still bring tears to the eye (and I am not talking about toxic pollution). Out of those materials, the pioneers laid down models for themselves in courage, independence, endeavour and the grace of the Bill of Rights. The hideous rhetoric about "this greatest of all nations" is painful because so much of that potential remains. Nor, in human history, has there been such a country and its code serving as beacons to peoples who did not have the language, the ticket or the faintest chance of being Americans.

That enormous process of immigration is still being accomplished. There is fantastic space still waiting to be filled; despite the present downturn, the country remains an ongoing economic miracle that could accommodate more people; with a scheme of rights that has done modest justice by a population that went from next to nothing to close to 300 million.

And yet, the underlying American response to that history ever since its great victory and imperial dawning in 1945 has been fear: alarm, driven sometimes to slaughter, at the stranger – whether Indian, black, or rationalist; the terror that space, home and prosperity, once achieved, might be ripped away; the debilitating notion that fortune is worth no more than the fruits of gambling, and is as insecure; the steady fuelling of the fires of unreason, so that every paranoid feeling grows into a "threat". Why else does such a country need so many guns, policemen and prisons? How is it that a land once pledged to free thinking and still the home of many great universities, libraries and museums finds itself in mounting dread of radical or adventurous thinking? Consider how a culture that once did so much in the invention of films, television, popular music and jazz has made those arts bereft of originality and increasingly drawn into the quarrels that pertain to the rights and the technology. How else does one explain such a turning away from opportunity except in terms of overwhelming fear?

Perhaps you feel hyperbole has set in – for surely the US is a country in which such a diversity exists that outstanding pieces of the heroic, the noble and the virtuous must be observed every day? Yes, that's still so. A lone climber in Colorado last week, finding himself trapped as a boulder moved, cut off one of his arms below the elbow, fashioned a tourniquet, then walked seven miles to find help. In San Francisco, I heard the city's orchestra, under Michael Tilson Thomas, deliver Mahler's 9th Symphony with a grandeur and tragedy such as I have never heard. Daniel Patrick Moynihan, who recently died, a severe loss, was generous, wise, urbane, teasing and utterly American.

And yet, in this same land, teachers (already fearful of being eliminated in budget cuts) are afraid to fail students who lack the capacity or the right to graduate from high school; some doctors are afraid to be involved at legal abortion clinics because of the risk to their careers and their well-being; the difficulties of obtaining moderate health insurance compels more people into a gamble with their lives, the statistics of accident and the likelihood of infection; the urge to vote and to be active in politics are in such retreat that reports on voting figures are a national scandal; and the US prefers not to ask why it is now regarded with such dismay in the rest of the world.

The list of anxieties could go on, and it defies the woeful US orthodoxy that this is the best of all countries. Or needs to be. Whereas the US knows less and less about the outside world for Americans were virtual-travellers long before that became a possibility. They were afraid to travel with open minds. A melting pot of diverse languages, we now cling to our uniquely drab, misspelled English. Yet that vulnerability will only be the more exposed as the country finds itself in an occupying position in more parts of the wayward or misled world.

Cheer up? By all means – I have just read the life of a great American, W C Fields, a man of such generosity that, though he could never adequately amuse or treat himself, he still gave his life to entertaining others. He was a genius who saw that entertainment was not just fun, or silly, or decoration: it went to the heart of life. So Fields made a show of himself in which laughter was thoroughly allied with foreboding, loathing of children and animals, horror at the notion of women, et cetera. He was a misanthrope who dreaded everything except a quiet afternoon and a flagon of gin, and who made his fears hilarious and instructive.

That's where irony comes in. There are, truly, many things to be afraid of. The city where I live, Los Angeles, is on a great fault in the ground. You can't take the gamble out of life – and you shouldn't try. But American fear has made such pacts with decency, respectability and good taste that it begins to resemble habit.

Here is my last Cassandra observation: that fear – fear of Aids, fear of danger, fear of responsibility – has begun to ensure two kinds of sex in the United States. There are sexual relations, legitimate, married sex, child rearing and so on, succumbing to habit, custom and safety; and the other kind – illicit sex. Am I endorsing that kind of outlawed sex? To do so seems anti-social. Yet the US was once a revolutionary entity. My own fear is that, as it comes into its own – in terms of power, it develops a helpless insecurity enough to chill all the flowers of empire.