At the very end, Jack Kennedy's voice sailed out over the stillness of the library landscape and left a wake of goosebumps across the surface of the crowd. For a few minutes politics was replaced by a profound and silent sense of loss.

The symptoms were as familiar and predictable as the lump in the throat, the hand at the mouth, the tears. But all weekend, after many of the Kennedy people had gone home and the city was basking in Indian summer, I kept wondering about the loss.

What is it Jack Kennedy's words invariably tap in so many of us? What button is pushed by the sound of his voice? Is it a sense of loss for the man, or for a time in our lives, or for a time in our country's life?

I was in college when Kennedy was president. I was 22 years old and three months into my first job when he was killed. Although I was as realistic as most of those whose family business is politics, my own youthful sense of possiblities coincided with Kennedy's call to get the country moving again.

Now, according to all the actuarial tables, I am in the middle. Those of my generation have lived through 16 years of public life that sounded alarm bells across the textbooks: Vietman, Watergate, the energy crisis, inflation. Also we have lived through 16 years of private life in which most of us have made the major decisions about work, children.

Today, like many of my generation, I sense that my choices no longer range from a to z, but perhaps from a to e. This is not a complaint, just an observation.

In mid-life most of us feel these limits. We don't squander our energy; we allot it with care. We call this maturing. The young call it aging.

But when I hear his voice, his words, I feel a loss. Is it loss for a time and attitude of life that I have outgrown as irrevocably as I have outgrown naivete? Or is it loss for a time of this country's life, before lowering our expectations became our best protection from disappointment?

I have heard friends wonder about this in other contexts. It is not merely a question about our past and present. It may very well determine the future -- whether a "call to battle" rouses us or repels us as a foolish children's crusade.

Are we just playing possum, as Carly Simon sang, or have we really changed?

Before Jimmy Carter left Boston, he said that he and Ted Kennedy differed on little -- only spending and arms. But I heard other differences on the platform that day, different approaches to our psychology.

Carter talked about living in a time of "limits" and an age of Hard choices." He said that "we are struggling with a profound transition from a time of abundance to a time of growing scarcity in energy."

Ted Kennedy talked about challenges that are opportunities, and spirits that "soar". About Jack he said, "He understood that America is at its best when the nation is on the move, when ideas are on the march . . . . He filled America with pride and made this nation young again."

Both were, of course delivering their own Saturday sermon versions of the Jack Kennedy text. But they may have opened a dialogue that is really familiar to those of us in mid-life -- between limits and opportunities, fiscal realities and challenges, hard choices and historical purpose.

Before the opening of the library, a cast of Jack Kennedy's people had spread out through the city talking to high school students. Historian Arthur Schlesinger put this argument another way at my former high school. He said, "I do not see American political history in terms of liberal versus conservative, but rather in terms of exhaustion versus vitality."

Clearly he associated Jack Kennedy with vitality, Carter with exhaustion and Ted Kennedy with renewed vitality. The senator echoed that in Philadelphia when he said Americans want Actions, not excuses." But those of us who were young with Jack may not see it quite that simply.

Whether we back Kennedy or Carter may depend on whether we see our own political history as an energy cycle or as a progession. It may depend on whether we regard "limits" as a term of mid-life depression -- an excuse for defeat -- or of mature realism. Whether we see Carter's "hard choices" as excuses" or facts. Whether we see "opportunities" as renewed hope or youthful delusions.

In short, it may depend on what we were mourning when we heard Jack Kennedy's words on the Boston shore.