<p> It was a situation from which half-hour television comedies are made. "<i>Marcia!</i> In tonight's episode, Marcia Green's warm and winning and wise and wonderful Jewish family reminds her that she is thirty-five, divorced, and childless." </p> <p> That's Marcia on her close relations. True, she's one of the best speechwriters around in the tough world of New York's smoke-filled rooms, but her family wants something else for her. No, not that Irish person she's living with. Another doctor, or at least a dentist. </p> <p> But Marcia claims she's happy, getting plenty of the two things that exhilarate her most: sex and politics. She's not looking for commitment, and certainly not looking for a wealthy Harvard-educated man-about-town who is every mother's dream. Yet as wise mothers everywhere are fond of saying: <i>you never know</i>. </p>