WE AMERICANS SEEM to have a fondness for holding the mirror up to our lives. From the college bull session to the millions of soul-searching monologues unloaded in countless psychiatrists' offices, we are constantly concerned with whether our lives are yielding the maximum of satisfaction with the minimum of pain. Gail Sheehy's new self-help book, Pathfinders, for which, with paperback rights, she received a $1 million advance, is bound to find an eager audience.

And it should. This is a powerful book based on four years of formidable research across America and Europe, and it is peopled with interesting men and women who, after encountering adversity, break out of a constricting mold to risk change and loss for a new life. Some accomplish this by abandoning the comfort and security of safety for a cause beyond themselves. All are real people taken from the 60,000 who filled out extensive life history questionnaires, which Sheehy had sent to selected groups and also published in Redbook and Esquire. It is a measure of Sheehy's skill that hardly one of her subjects seems too good to be true.

Sheehy's way with words is more than just fortuitous. For Pathfinder, it is essential. This heavily documented, 494-page book is first cousin to a textbook. Pathfinders, billed on the jacket as being about "Overcoming the Crises of Adult Life and Finding Your Own Path to Well-Being," eventually leads us through a review of history's major cultural swings and, in less skillful hands, might have been daunting. Its scope is large, and it is stuffed with the theories of anthropologists and historians. It is also completely fascinating.

You care about the people who walk through these pages. Another turn of the wheel and they might have been you, might still be you since nothing is certain. These people speak with voices that cut right through you. "I'm scared to death to do this," cries the wife of a field engineer who quit General Electric over doubts of the safety of a nuclear installation, "but . . . I don't want to be dead inside a body that goes on walking around." When Sheehy introduces us to these people, she makes us see them intimately. "There was a big sky sprawl to his speech," she says of one.

The concern of this book is to explore what makes pathfinders. (I wish Sheehy had found a better term for these people, one which did not trigger association with James Fenimore Cooper, but none comes readily to mind.) The qualities of pathfinding are not innate, she tells us, and we might all ualify. The transformation into a pathfinder usually takes place after some life accident which changes the rules and causes us to seek and risk uncommon solutions to struggles. Change and risk are frightening. "Many of us would rather risk even death than change," she says, "and we stand ready to employ our faculties overtime to avoid acknowledging those changes taking place right under our noses."

Sheehy takes us into the lives of many people who have had the courage to fail and gain from the experience, to reassess, to stretch and shed an old skin. Many wives of the hostages had this experience; so do some desperate men who have been passed over on the corporate ladder. Ordinary people gathering the courage to rise above physical handicaps, women shucking loveless, crippling marriages, successful men reexamining values in mid-life--these are Sheehy's pathfinders.

You don't need any inborn trait to transcend life accidents, but it helps to have a support system of friends. Sheehy is particularly poignant when she recounts the moment when a close friend confides to her that her husband is demanding a divorce. In every word of the bleak dialogue atop a ski slope, you feel the value of the friendship the two women share. "If the risk of change and loss is essential to the process of pathfinding, friends are the haven," says Sheehy. People of "high well-being" in the questionnaire (included in the book) reported twice as many close friends as the average person.

What gives this book its power is the frankness with which these people open their minds and hearts to expose their frustrations and pain. The book does not work as well in its last section, in which Sheehy interviews the famous who have transcended pathfinding to become "pathleaders." But if we have lost the ordinary people we can identify with, the picture she paints of America's progress from Puritan ethic through the laid- back '60s to the age of the televangelist is one of the best portions of the book. America needs, she tells us finally, the true revitalization which will only come when we are united around a transcending moral issue. ELIZABETH C. MOONEY, a Washington writer, is the author of Alone: Surviving as a Widow.