ONLY A FEW totally honest accounts of a human life exist. That's not because people are lacking who would like to tell the truth. (They probably are a minority.) It's because you can't tell it unless you know it. Biographers, not being mind-readers, never know it all. People who write their own lives are only slightly better off. To see the truth of your own life you must first have gotten beyond all illusions about yourself, and probably about the world, as well. Few of us do.

Diana Athill is one of the few. She is also a gifted writer -- and, if one may judge by this book, an enchanting woman.

Instead of a Letter is the story of her life up to the age of 43. That is, from 1917 to 1960. It is not a typical life. It contains more privilege, more suffer (internal, not imposed), and in the end acuter happiness than is the common lot. And yet, at least to me, it seems like the revelation of a whole sex. Short of being born a woman myself, I don't know where I would have gotten a greater sense of what it would feel like to be female than I did from reading Instead of a Letter.

Diana Athill is upper-class English. She grew up mainly in her grandmother's house, which had 20 bedrooms, a park, and a thousand acres of land attached. She loved life there, with its ritual, its servants, even its characteristic English upper-class discomforts, such as no heat. ("'My sponge is often frozen solid in the morning,' I remember boasting to some less hardy, less fortunate child.")

At 15 she fell in love with an Oxford undergraduate named Paul, who had come to the estate to tutor her brother. At 19 she became engaged to him. They also began to sleep together, a more unusual event in 1936 than it might be now. A couple of years later, soon before thy were to be married, he broke the engagement in a way so cruel that it caused her to lose all confidence in herself. (He didn't mean to be cruel; he was just the sort of man who hates awkward scenes.)

For the next 20 years she led a kind of half-life: plenty of affairs that were sure to lead nowhere; a successful career, but she often slept 12 hours a night on weekends, to be rid of the time; a general sense of waiting, but of waiting for nothing in particular except the slow arrival of old age.

And then at 41, a miraculous reversal. Having almost by chance started to write stories, she entered a contest, and she won it. Soon after, she began her first serious relation with a man since she was 22. The book ends on a high note.

HERE, in short, is the plot of many a romance novel. Here is a life begun in joy, brought to sorrow, and then when least expected returned to joy. The chief difference is that in the romance it would have returned about 15 years sooner, while she was still able to have children and a long, long future.

So where do the honesty and the overwhelming sense of female life come in? Under the plot. In the details of the plot.

Take, for example, the night that Paul first kissed her. She was barely 17, he a very sophisticated 21. They happened to meet at a dance where each had gone with a group of other people. She knew plenty of boys her own age. "I never thought of holding them off for Paul's sake: the gaining of experience was too valuable and exciting in itself to be rejected. He was the man I loved, he was the man I was waiting for, but meanwhile if anyone else wanted to fall in love with me, or to kiss me, or to tell me I was attractive, I would welcome it greedily. It was pure chance that it was, in fact, Paul who kissed me first. By then I had been waiting for him for two years, which anyone over 25 should read as five, or eight, or ten."

Paul perceives her readiness, spends the evening with her, eventually takes her out to his car. "When he turned my face up and kissed me on the mouth, we were both surprised: I because his lips were cold and a little sticky whereas I had expected them to be warm and smooth; he because mine were hot and parted whereas he had expected them to be like a child's. He told me later that he had thought, 'The little devil, she has been at it already, this is not the first time,' but it was."

When Paul brings her home, very late, her mother is still awake, and furious. Under cross-questioning, she admits to having been kissed.

"'Oh,' she said, and I could sense the clutch of fear in her stomach, 'Did he just kiss you, or did he -- are you sure he didn't mess you about?'

"I could not strike her because she was in bed and I was standing some paces away. I could only mutter savagely 'How could you say that!' and slam out of her room thinking, 'Damn her, damn her, damn her!' I could still feel Paul's dinner jacket against my cheek, those surprising lips, and his hand lightly on my breast where my own hand held it; I was still wrapped about with the most important moment of my life, and she had said 'mess you about.'"

Then she ends the chapter, "Poor parents, what are they to do?"

I'm afraid one example won't convey the marvelous frankness and immediacy of this book, let alone the calm wisdom with which Diana Athill at 43 looks back on her life and understands its every nuance. There is no room to quote the 50 or so other examples I would like to, such as her account of her first wartime job in England, or her wonderful analysis of a Greek man with whom she doesn't have an affair on Corfu, or her relation to rooms in which she lives and how she decides when it's worth keeping them neat and when it's not. About all I can do is say there were more than 50 times I sighed with pleasure at how well this woman writes, how acutely she perceives.

Not everyone, I admit, responds to the book as I do. When it first came out in London in 1962, the reviewer in the Times of London (anonymous in those days) was appalled. Admitting the brilliance of the writing, he deplored the honesty. "She will either horrify or embarrass those readers who believe in the desirability of clinging to some shred of reticence."

But that was in another country, and long ago. I think most American readers now will find the book pure joy. My one complaint is that Diana Athill has yet to publish the second volume. I long to find out what has happened to her since.