One day last week Ed Koch left his Greenwich Village apartment to take the M-6 bus downtown. About the same time he was being sworn in as mayor of New York City, my friend Carol was turning down a job as a top executive of a New York corporation.

On the surface, these two events seem to be totally unrelated except for the fact that they took place in the same city. But I don't think they are. You see, Ed Koch is a bachelor, and my friend Carol is married and a parent, and there's a difference.

No, this isn't a story that ends with a one-line complaint from Carol: "If it hadn't been for you, I would have been a star." (Or a mayor, for that matter.) Nor is it a story of discrimination. Her husband didn't put his foot down. Her parents didn't form a circle around her shouting, "Bad Mother, bad" until she capitulated.

Carol chose. She wanted the promotion so much she could taste it. But the job came with weekends and evenings and traveling attached, and she didn't want to miss that time with her husband and sons. She couldn't do both. Knowing that didn't make it any easier.

Carol isn't the only one I know making these decisions. Another friends refused to move up a rung on the professional ladder, because it would have meant uprooting his family and transferring his wife out of a career of her own. A third couple consciously put their careers on the back burner in order to spend time with the family they'd merged out of two previous marriages.

These were not bitter choices, but tough ones. As Carol said, it isn't possible to give overtime at work and decent time at home.

Once it was normal for a man to devote his energy entirely to his work, while his family was taken care by his wife. Once men led the public lives and women the private lives. Now that gap is closing, and another one is growing between family people and single people. Everywhere it seems that men and women who care the most about the their private lives are living them that way, while the single people have become the new upwardly mobile.

In Washington, you can see the difference. There, a 28-year-old bachelor such as White House aide David Rubinstein works more than 16 hours a day and eats vending-machine meals, while a guy like Rep. Lloyd Meeds (D-Wash.) decides not to take his family through another congressional election fight and drops out. There, despite the attempts of the Carters to encourage family time, the government still runs on excess. As the observer puts it, the only way to get the work done is to be single or to have a lousy marriage.

In New York, the successful politicians (aside from Koch) now include Carol Bellamy, the single head of the city council and Andrew Stein, the divorced borough president. The governor is a widower; the liutenantt governor is legally separated.

All around us the prototypical workaholics are single, with Ralph Nader leading the Eastern division and Jerry Brown bringing up the West. And in the U.S. Senate last year there were enough divorces to justify legal insurance.

I don't think that this is something "movements" or legislation can solve. I am reminded of the moment in the movie "The Truning Point," when Anne Bancroft and Shirley MacLaine realize that they both wanted it all. There two women hadn't chosen in their lives between work and family in the classic sense, but between workaholism and family: between the sort of success that demands single-minded devotion to a goal and the sort of "balanced" life that includes family and work, but precludes overchieving. In the end the star was a bachelor.

The decisions they faced are the rock-bottom ones, the toughies. How do you devide the pie of your life - your own time and energy?

Today, the cast of characters is changing. It isn't only men in high-powered work lives and women at home. But the choices have remained the same. There seems to be an inherent contradiction between the commitment to become No. 1, the best, the first, and the commitment to a rich family life. A contradiction between family-first people and work-first people.

The irony is that we need decision-makers who care and understand about children and private lives. And I wonder how we will find them if the room at the top becomes a bachelor pad.