Happy birthday to them?

Today is Bill Clinton's 50th birthday. With him a generation comes to mature years. And not just any generation: today is the birthday of the most analysed, the most derided and quite possibly the most significant generation in American history: the children of the post-war baby boom.

President Clinton's Republican challenger, Senator Bob Dole, is one of the deriders. The baby boomers, he said in his acceptance speech at the Republican convention in San Diego last week, or at least those of them who work for the Clinton administration, "never grew up, never did anything real, never sacrificed, never suffered and never learnt".

Dole was expressing the bewilderment and outrage with which the older generation, those who experienced the privations of the Depression and the dangers of war, in which Dole himself was wounded, has always looked on its juniors.

He was also perhaps gambling that the generations younger than the baby boomers, who missed out on the relatively effortless prosperity of the Fifties and the excitements of the Sixties and whose experience of the present decade has not been a bed of roses, may share the older generation's resentment of the generation in between.

So who are the baby-boom generation? What is it about their experience that generates such fury? And why are they so important?

When the Second World War ended, the United States demobilised armed forces of more than 14 million men and women in little over a year. With victory won, both men and women knew exactly what came top of their priorities. Alfred Eisenstaedt's famous photo of a kiss in Times Square, used on the cover of Life magazine, caught the mood exactly.

For the most part, the men who came home were going to raise a little hell. They were going to get them a gal. And then they were going to settle down, in the newly accessible suburbs, to raise a family.

That is precisely what they proceeded to do, to such good effect that they made a boom in babies just like the boom General Motors was making in cars. In the Forties, the American population rose from 131 million to 150 million. Those additional 20 million Americans came almost entirely not from immigration but from natural increase, and almost all of that in the second half of the decade. True, there was a lower death rate, caused by improvements in health care and hygiene; but the increase in population came mostly from a birth-rate that shot up from 17 per thousand to 25 per thousand.

So the baby-boom generation was a bulge in the shape of the American population, a little like the drawing in The Little Prince of a boa constrictor that has swallowed an elephant.

But the importance of the baby boom was not just demographic. For the swollen American birth-rate of the late Forties coincided with the economic boom of the post-war years. American incomes rose sharply, and consumer income rose sharpest of all: by almost 30 per cent in the four years after the war.

People had skimped in the Thirties, when unemployment was more than 25 per cent. During the war they had gone without because they were in uniform. Now they found that houses, cars, kitchen appliances and all the other things - including higher education - they had only dreamt of before the war could now be theirs.

This was the age of the new, mass consumer market of EJ Korvette's cut- price department stores, of the spread of supermarkets, and of the new Levitttown suburbs. William J Levitt was called "the Henry Ford of housing", and he aimed his houses specifically at the returning soldiers and sailors.

The first ad in the New York Times said: "All yours for $58!" Actually the houses cost about $8,000, but that was all you had to put down. "You're a lucky fellow, Mr Veteran," the ad went on. "Uncle Sam and the world's largest builder have made it possible for you to live in a charming house in a delightful community without having to pay for them with your eye teeth."

While the fathers went off to work for good union wages in the new factories or the new offices downtown, the wives stayed at home and raised babies. As Betty Friedan wrote later in The Feminist Mystique, at first women did not realise how much they were missing in this isolated child-centred world, so different from the crowded city neighbourhoods their mothers had known.

"As she made the beds, shopped for groceries, matched slip-cover materials, ate peanut butter sandwiches with her children, chauffeured Cub Scouts and Brownies, lay beside her husband at night, she was afraid to ask herself the silent question: 'Is this all?' "

It was Adlai Stevenson, twice unsuccessful Democratic candidate for president, who gave a name to the cause of this dissatisfaction, both for men and women. He called it "the revolution of rising expectations".

The post-war parents, the first generation in history in which the majority escaped from poverty, were happy enough. And their children, growing up in the Fifties, were ecstatic.

Tom Wolfe recalled what it felt like to drive Dad's new car with its V8 engine along the new superhighways: "Post-war American suburbs, glorious world! To be Superkids! The world's first generation of the little devils - feeling immune, beyond calamity. One's parents remembered the sloughing common order, War & Depression - but Superkids remembered only the emotional surge of the great payoff."

By 1965, the more fortunate kids of the baby boom were beginning to go to college. And there, they underwent a strange transformation. The cartoonist Jules Feiffer summed up the generation gap in one of his wordy but wonderfully perceptive cartoons. The father says: "When I was a kid I lived in a slum, I had to quit school at 12. And I used to say to the world, I'm out to buy me a dream! A small house in the country! Yeah! A white picket fence! A dog for our kid! Yeah, world, yeah! An American dream."

So now the father makes $50,000 a year, enough to keep a second wife and a son who has owned five different cars since he was 16. And the son says "I'm drowning!"

So in the Sixties, the sons and daughters of the dream dropped out, tuned in and turned on. The decade has become a stereotype, but enough of the image is accurate enough. Oedipally, the baby-boom generation rebelled against the gigantism, the complacency, the impersonality of the immensely successful society that had brought them up. They took to pinning on badges taken from IBM cards, saying "Do not staple, fold or mutilate!"

Taken from behind the white picket fences of the suburbs and dropped into the inner-city neighbourhoods that surround so many great American universities - Columbia, Berkeley, Chicago - they saw for the first time the seamy side of American life. They rebelled against racial injustice, against the military, against their parents, against rules and regulation, against prudence and rationality itself. Their ambition turned into idealism, their confidence into a belief that they could change America and the world.

The superkids of the Fifties still felt the "emotional surge". But now it was turned against what they saw as the harshness and the banalities of the very economic machine that had freed them from serious financial worries.

There was at first a political rebellion, mainly on the issue of the Vietnam war. It did not last long. For most baby boomers, it was quickly replaced by the search for new ways of living. For some, this was self- indulgent; for a few, self-destructive. For most, the spirit of the Sixties lived on only as a looser, less uptight manner, a taste for marijuana - even for those, like the President, who didn't inhale - for Western clothes and for rock music.

The Sixties did not end in political revolution, and even the lifestyle experiments of the decade lingered on as fashion rather than fundamental change - except for one. The attitudes and expectations of American women were drastically, irreversibly changed. Their circumstances have also changed - though, as any one of them will tell you, not enough.

So if the baby boomers spent the Fifties as superkids, and the Sixties as rebels in any number of causes and as drop-outs (some permanent, far more temporary), they spent the Seventies in carrying out, or going along with, a sexual revolution against the world of the Fifties suburbs.

As thirtysomethings, they spent the Eighties being, or trying to be, young, upwardly-mobile urban professionals. The emotional surge of the superkids, the rebellious individualism of the Sixties, were focused on the new goals of yuppiedom.

So in the Eighties, the baby boomers became the "me generation". That does not mean they became monsters of egotism. But for many, self-expression gave way to acquisition, self-indulgence to focus, idealism to ambition.

For in the meantime the baby boomers had passed through another, conservative political revolution. In some cases, there was a literal jump from far left to far right, or at least from cultural revolution to hip capitalism; in the extreme case of Abbie Hoffman, the bearded clown of the counter- culture whose followers called themselves the Youth International Party and who became a bond trader, it was a jump from Yippy to Yuppy. But for most of the baby boomers, as for Bill Clinton, the Eighties were a time of fitting the ideals and ambitions of the Sixties to the realities of a newer, more conservative age.

Meanwhile, a new generation was coming along behind the baby boomers, and with a far less breezy and optimistic view of its prospects. For the first time in American history, surveys show, there is a generation of Americans that does not expect to live better than its parents.

The new mood may have been caused by the fact that for 20 years incomes, after taxes and in real terms, stayed virtually static. It expressed itself in a perceptible shift of the political centre of gravity to the right.

For baby boomers who worked in business, at universities or in the law, the adjustment to a new, conservative world was not too hard. Neither martyrdom nor recantation were required, only going along with the new business ethos. Only for those, like Bill Clinton, who were politically ambitious, were the dilemmas sometimes agonising. To be politically effective, it was necessary to move a long way towards conservative ideas, as Clinton and the New Democrats have done.

But Clinton, at 50, has not forgotten the upbeat experience of his generation, nor has he given up on its ideals. The Democratic convention in Chicago will be his opportunity to once more set up its standard, in opposition to Bob Dole, the oldest presidential candidate in American history, and his grittier vision of the American future. Clinton's own view of the world may not have changed so much since 1975, when his old friend Robert Reich, now Labor Secretary, reported on the fledgling Arkansas politician's mood to fellow Rhodes scholars of the class of 1968.

"He says", Reich wrote, "he is concerned that he does not really have a good grasp of what is happening in this country, where we are going, and what we can do to make it better. So like most other people, he lives and works as best he can."

The baby-boom generation always wanted to make the country better. It is just that they have changed their minds so often about what "better" means.