COMPOSITE WOMAN (actually, several women at different times) is coming to lunch. There she is entering the restaurant. She's the pretty one. Dark hair. Medium height. Nicely dressed. Now she is taking off her coat. Nice figure. She sits and begins with a status report. The job is just wonderful. She is feeling just wonderful. It is wonderful being her age, which is something between 27 and 35. And the fact of the matter, in case you should wonder, is that there is a new man in her life and he, like everything else, is truly wonderful. Then she looks down.

Is there something wrong? Composite Woman says nothing. I ask again. Again she says nothing. Finally I do the you-can-talk-to-me bit.

"Off the record?"

"Absolutely."

"I want to have a baby."

Sometimes, the Composite Woman is married and sometimes she is not. Sometimes, horribly, there is no man in the horizon.What there is always, though, is a feeling that the clock is ticking. A decision will have to be made. A decision that will stick forever. You hear it wherever you go. Women all over are singing their own version of September song.

I've gone around, a busy bee of a reporter, from woman to woman, the ones in the office and the ones I meet elsewhere. Isn't it interesting. I say, this business about the biological clock? How do you feel about it?

They say, a few of them, that it means nothing to them, that if the mood hits them to have a child, they will adopt. From them, you get the message: There are already too many children in the world. I thought that once, too. Then I thought there was room for one more - mine.

Anyway, most of them did not say that. Most of them said that they could hear the clock ticking. Some talked about it in a sort of theoretical sense, like the woman who said she wanted five children and didn't even have a boyfriend yet. She had to get something going, she said, and you could tell that she resented the fact that a deadline had been imposed on her. Some women talked about it the way farmers talk about the weather, with a sort of resignation. Unfair, yes, but out of their control - an important word. Up to now, they've been able to postpone it to go to college and have a career and do all the things that men traditionally have done and now they face this biological clock. One woman who has definitely decided not to have children put it in strong terms.

"It's unfair" she said. "It doesn't make me resent men: it's just unfair. Everything has changed since I was 20 years old. And I know enough now to be sure that I don't know how I will feel 15 years from now. Fifteen years from now, I might desperately want a baby."

I was being wonderfully dispassionate and reportorial and every inch a gentleman, but she caught an edge in my voice and opened up on me.

"You don't want to believe it," she said. "You resent it. You resent it. Every man I know resents it." And then she named the men, men I know, good men, noble men, men of vision, open-minded men who were not your basic male chauvanist pigs. They were, in short, men like me. She gave me one of those you-know-I-am-right looks and I did know she was right.

But more than that, I recognized that I had been something other than a dispassionate reporter when I was going around asking women about the biological clock. I was getting aid and comfort from their answers.

There was something about their situation that showed, more or less, that this is where liberation ends. This is where a woman is a woman - biologically, physiologically, uncontrovertably different. Don't get me wrong. We are not talking about recognizing a difference and being glad that some of us are on the "right" side of it - the side of Charlie Chaplin and Pablo Picasso and all the other senior citizen fathers, the side that heeds no clock.

But there is something else here: once you recognize the difference, you also have to recognize that the difference produces advantages and handicaps. Little about it is simply neutral. This is important because there is now something in the air about women having won their fight for equality and even something about how it was always harder to be a man, anyway. But there are some things we never had to worry about.

Like the ticking of the biological clock.