THERE IS A VACUUM at the center of America's political life. Surrounding it are contending individuals and factions which have demonstrated for over a decade that they are incapable of filling the void. Many of the individuals are clever, committed, politically astute and close students of the nation's history, current and past. Many of the factions, particularly toward the poles of right and left, have innovative, occasionally startling ideas to offer as unifying themes around which a new majority can be created.

But a vacuum it remains in late 1980, and the coming presidential election does not offer much room for believing that the results will change this fundamental fact of contemporary existence. On the strength of David Broder's fine piece of reporting and analysis, Changing of the Guard, there is no clear evidence to suggest that it will be filled by anyone or any group over the short term beyond election day either. What is clear from his interviews with scores of activists is that the problem is understood and troubling to virtually all of them, whether they represent the old politics of the New Right, the newly enfranchised and mobilized minorities or the resisting adherents of the old verities. The consensus around which the center-center left rallied and from which it ran the country for decades has disintegrated, and a new one has yet to be formed in its place. That said, there are almost as many in the emerging cadres of leaders and would-be leaders who abdicate responsibility for a solution as there are those who cling fiercely to wildly disparate prescriptions for one.

Border presents them all in a book that could have been trivial in one way or ponderous in another. Instead he manages a portrait of the new leadership generation which is as rich in detail as the generation itself is varied and as blurred in its overall impression as the men and women he has examined turn out to be when viewed as composite.

One mildly critical note here. It is somewhat troubling to have wrestle with a conceptual framework which includes anyone between 25 and 50 as participants in the guard-changing process. As a rapidly aging 45-year-old who worked at least peripherally in several of the movements which Broder correctly identifies as central to the new guard's outlook and perceptions. I must confess to having far more in common, intellectually and emotionally, with those he sometimes seems to believe will be on the ash heap of history by the late 1980s than with those who once shrilled that my contemporaries could not be trusted because they were over 30. What is more, I suspect that a large number of people my age feel the same way.

Or perhaps that is only my personal version of the midlife crisis, a concept invoked frequently by Broder's subjects to explain the nation's current flounderings. Reading their faithfully recorded interpretations of what is going wrong in America and how it could be set right, it is impossible not to be reminded of the story of the blind men who were asked to describe an elephant after each was allowed to feel only one part of the animal's anatomy. Too many of those who may participate in changing the guard see only the trunk, the tail, the leg or the rump of the vast entity which is our nation. Too few have a wider and fuller vision which incorporates the parts in a coherent whole; if they do have a vision, most lack the courage or energy to pursue it, perhaps intimidated by the single-issue wreckers or the supporters of a status quo that never was. It is a troubling conclusion, but one which Broder makes inescapable in long quotations from the people themselves no less than in his own insightful commentary.

And yet, how bright so many of them are and how involved so many of them have been in the major events of the past two decades. For those who have lived through and as a part of those times, the temptation will be overwhelming to thumb from the index through the book's pages, seeking the names and words of particular heroes and heroines, villains and sellouts. And, regardless of ideology or race or class, at least some of those each reader seeks can be found in Changing of the guard. (One exception: nowhere is attention paid to the newly politicized religious fundamentalists as a force in the coming years, although their significance is no more a temporary phenomenon than was the civil rights revolution 20 years ago.) The volume is the product of two years of research and writing, of individual and group interviews, of history reading and (as a distinguished reporter and columnist for The Washington Post) history writing. It is far more than a journalistic snapshot of a moving train. Broder offers a sense of the journey itself, where the nation has been and where various forces have been taking it, interspersed frequently with interviews of his fellow passengers.

It is right and proper in a book of this sort to let the story tell itself as much as possible, which for the most part meant letting the various representatives of the group Broder finds important speak for themselves. But the occasional glimpses he allows of what he thinks of some of them makes me long for far more of that particular red meat. Having seen them close up, not only in writing this book, but also in the years that precede it, he could have helped us all by sharing his insights as to which were closer to being charlatans than fit recipients of the public's trust. Few are better qualified than he to offer such judgment; too many of us must rely on that imperfect filter, television, or an occasional gold mine of information such as Changing of the Guard to help us to decide where to place our allegiance.

Not that he shrinks from assessment. Two of his concluding points stand out, contradictory though they may sound when taken out of context. First, toward the middle of the final chapter, he asks a disturbing question about the group as a whole:

"When have they moved ahead of public opinion, and used their intellectual, political and rhetorical skills to prepare the nation -- or the segment of it that is their constituency -- for the challenge they can see looming ahead?"

And then, the coda of hope:

"But thinking about the people I met in writing this book, I feel some confidence that this generation has not lost its sense of direction or its capacity for leadership. On the big questions they have faced in their adult lives, their instincts have been more right than wrong -- and more right than those of many of their elders."

Which is what we must collectively hope will prove true in the coming years, when the inexorable fact of the post-World War II baby boom will produce its inevitable political results. A nation, no less than nature, abhors a vacuum, and the one which exists at the center of our governing institutions will eventually be filled. The question is, how soon and at what cost if long-delayed. In Changing of the Guard, David Broder has given us a far better idea than we had before of what rough beast slouches toward this policical Bethlehem to be born. That it is not finally a definitive idea says nothing about the considerable skill and perception of the observer and almost everything about the state of our society today.