AMERICA'S SECRET ARISTOCRACY By Stephen Birmingham Little, Brown. 334 pp. $18.95

Stephen Birmingham, the intrepid and somewhat wide-eyed chronicler of life in America's privileged classes, herewith turns his attention to the oldest and in certain respects least known of them: the "Protestant Establishment," as E. Digby Baltzell called it in his book of that title. This is the "old regime" that, as one of its members once wrote, "does not believe that publicity is necessary to social success," but that from behind the scenes has played a powerful role in shaping the nation and its history.

That these people prefer to live and work in relative obscurity may seem a frightful anachronism in this age of self-assertive celebrity, but it's an anachronism with which the members of this class are comfortable; as Birmingham observes, the old upper class "has been allowed to retire into the privacy, even secrecy, that it much prefers, and it is even grateful for the new breed of society, which thrives on publicity and cannot seem to exist without it, for having drawn the attention of the media away."

Birmingham's book is of course itself a form of publicity, but one that its subjects are unlikely to resent. For one thing it is in virtually all respects deferential if not obsequious; he regards the old guard as upholding "the true standards of a true aristocracy -- standards of cultivation, of intellect, of duty, of generosity of spirit, standards of doing one's best." For another, Birmingham makes little real effort to drag the old guard's skeletons out of the closet. And for yet another, the book is entertaining and perceptive -- once over lightly, to be sure, but lightly with a deft touch.

Though this old aristocracy is not uniformly white, Anglo-Saxon and Protestant -- as Birmingham notes, there has been a modest amount of intermarriage with Jews, Catholics and, quite infrequently, blacks -- it is of a distinctly British and Scottish cast: "... like the members of the Royal House of Windsor since Victoria's time, American aristocrats in their private lives often convey the impression of being rather ordinary people, neither particularly intellectual nor witty, committed to their friends and to lives that are comfortable and familiar, people who are not remarkable for being anything other than what they are and were born to be -- and who are remarkable only for not having to demonstrate, or prove, who they are."

Although this self-confidence can, and often does, deteriorate into snobbishness and smugness, at its best it enables the "secret aristocracy" to "live formally, without standing on formalities, to live pleasantly but not pompously, politely and not assertively, and never to bemoan the loss of an older, more rigid pecking order based on wealth alone." Though many in the old guard are quite independently wealthy, many others are not; yet to neither the quietly rich nor the genteelly poor does money assume the central, obsessive position that it does for those whose lives are chronicled in Manhattan, inc. and Vanity Fair.

What often does assume great importance in their lives is ancestry -- not mere ancestor worship or genealogical fixation, though traces of both surface from time to time, but a sense that there are lessons to be learned from those who went before. A member of the old guard puts it quite nicely:

"I was brought up always reminded that I was a Livingston, and that I was expected to conduct myself as one. The family was always very proper on manners. And we grew up surrounded by family portraits, and so it was hard not to get the impression that these people, who had died two hundred years ago, were a part of us, part of the family, and that we were a living part of their past. And yes, of course there are upper-class values that show up in people, that are born into people, and that tend to come out in a more affluent class -- elements of taste, discretion, and morality which help to create people who know how to handle themselves, and who know how to accept responsibilities. It isn't something that was taught from my father's or grandfather's knee, exactly. It's something that, in a family such as ours, comes through almost by osmosis -- the knowledge that, as Livingstons, we were expected to rise to occasions."

Though to some ears that may sound elitist or complacent, it is in fact a remarkably concise and accurate explanation of how an aristocracy -- a "true aristocracy," in Birmingham's words -- perpetuates itself. This the old guard has managed to do, though in the process it has moved far away from center stage; it no longer plays a significant role in political life, and in business and the professions it has been supplanted by flashier and more assertive strivers. Its glories are in the past and its members, as Birmingham says, "are essentially old-fashioned people." But obviously he believes there is nothing wrong with that, and he is right.