Fear of Flying, written when she was 30, made Jong famous. The tale of a naive, neurotic heroine who allows herself to be walked over by unpleasant men in the name of self-discovery, it makes, like most of the fiction that followed it, a better autobiography than it does a novel.

But to see the same material approached from the same angle 20 years on leads one to wonder whether Jong has been confusing the creative and the cathartic for just a bit too long.

The first part of Fear of Fifty is just another basket-load of the same dirty linen that has already been well washed and beaten upon the sounding board of her readers' minds: how she married her second husband, the ABC psychiatrist Dr Jong, for analysis rather than love and to get over the trauma of being married to the first; the combative relationship with her family: all were faithfully documented in Fear of Flying, down to the details of the gold-leaf on the ceilings of her house.

Second, and arising inevitably from the first: so much of the book is an expression of Jong's personality as embodied by her fiction, that it is difficult to know whether one is judging Erica Jong or the literary merit of her work.

Jong, however, does much of the former for us. One of the charms of Fear of Fifty is that it is disarmingly candid and in her earnestness to tell it exactly how it was and is, strewn with admissions against herself - from her massive self-delusion over men to 'preferring to remain a writer who dabbled in motherhood' with an only child.

The third problem with this book is its unevenness: there are almost as many mad ideas in it as there are sane ones. One moment, Jong may be making some perfectly sober and reasonable contribution to the debate about the future of feminism in America, while the next she is asserting that 'make-up is no more optional for us than the veil for Arab women' or tucking up her daughter at night and telling her that she is protected by a shield of white light.

This is a great shame, because it has a tendency to undermine the validity of her sensible statements. Jong is emphatically worth listening to on the insidious American cult of political correctness, in the name of which dead white males are excised from university syllabuses and minority women writers 'touted whether they are good or not'; and formidable on the threat to freedom of speech posed by the lunatic fringe of extremist feminists, such as the militant Andrea Dworkin, who seek to ban and litigate over pornography or publications which depict violence against women.

Fear of Fifty, then, is not a conventional autobiography either in form or content. Anecdotes from the past are interspersed with bulletins from the present, family interviews with discursive pieces of social analysis; even poems (dreadful) find their way in between the confessions.

Yet somehow it is a far more reliable and immediate memoir than a catalogue of dates and events.

The initial preoccupation of the book is Jong's struggle with her intimations of mortality ('I am the older generation, and I am not always sure I like it'). Beyond that the focus fixes upon the misspent self-determination of her 'whiplash generation' of women, for whom divorce was its 'coming of age' and whose disorientation now lies in having had the questionable freedom to choose between career and family.

The most genuine and interesting of Jong's personal preoccupations are those that extend outside herself. Jong speaks regretfully of the 'spiritual hollowness' but it is sad to see Jong herself culturally adrift and casting about for a religion when there was one to be found all the time in her own backyard.

When she remarks that 'my family was fiercely proud to be Jewish, but not religious', Jong seems to be voicing the ambivalence of a generation of American Jews who are still close enough to the rich cultural legacy of European Jewry to benefit from it, but which, without their own religious input, is liable to become elusive to future generations.

Much of the book is taken up with Jong's dismay at the divisiveness rife in contemporary feminism. She is adamant that many women activists' vision of a 'future of socialist-realist art - happy feminists in blue overalls waving from shiny tractors . . . will not take us where we want to go'. To this end, Jong says: 'We need to unlock the staggering power of Eros in the female psyche.' And thus to bed, or Jong's favourite subject, as reflected by the large proportion of the book that is devoted to reliving that part of her adult life (that is, most of it) when she went through men as if they were going out of fashion.

All of this is highly entertaining, but it accommodates a serious agenda. Sex is at the root of Jong's literary raison d'etre and whether or not one admires the end result of her attempts to 'seduce the muse', this information is not only a perfectly valid exposition of the mechanics of creativity, but as inviolable as a person's character - which it is.

The ultimate irony of this book is that its rigorous objectivity should be the product of someone who has been obsessed in her life and literature with a search for a subjective truth. Out of a writer whose fiction is characterised by a refusal to step back from herself, a useful social commentator with a far-sighted world view is now emerging.