A Passage Through Middlescence : Gail Sheehy is back with a new report from the battlefield of aging : NEW PASSAGES: Mapping Your Life Across Time, <i> By Gail Sheehy (Random House: $25; 473 pp.)</i>

I cannot say it surprised me to read in Gail Sheehy’s “New Passages” that the syndrome she termed “Catch-30 for Couples” in “Passages,” her best-selling book published in 1970, could now be termed “Catch-40 for Couples.” Sheehy has long been established, after all, as a writer with a facility for what some might describe as beaming light on a murky path and what others may view as taking old cliches and making new cliches of them.

Further, “New Passages” is predicated on the notion that life has changed considerably since the appearance of the old “Passages,” a fortuitous circumstance for Sheehy, not to mention for us. “People today” she writes, “are leaving childhood sooner, but they are taking longer to grow up and much longer to die. . . . True adulthood doesn’t begin until thirty. . . . Fifty is now what 40 used to be.”

Elsewhere she notes, “The old demarcation points we may still carry around--an adulthood that begins at 21 and ends at 65--are hopelessly out-of-date. Many of us feel a little lost. We need some new markers.”

Which is where Sheehy comes in, predictably enough, given that her most significant successes (“Passages” and “The Silent Passage”) derive from that traditional American merchandising technique, “Find a need and fill it.”

“New Passages” is dedicated primarily to exploring what Sheehy calls Second Adulthood, and which she defines as the years from 45 to, as she puts it “85+”.

“How do we find our way to this exciting Second Adulthood?” she asks. “I see a brand-new passage in the forties, when the transition from the end of First Adulthood to the beginning of Second Adulthood begins.” Likewise, the reader may see, at this stage, the precise juncture at which pop psychology merges with the reading of a crystal ball. For while it is pretty to think that life can be plotted this easily, if it could be, there would be no need for the sort of books Sheehy offers the reading public.

As Sheehy sees it, the stages of a life, characterized with the pop phrasing that will be familiar to readers of her other work, are given as the Flaming Fifties, the Serene Sixties, the Sage Seventies. This absolutist approach to something as individual as life is, depending on your point of view, comforting, deadening or just plain absurd. For myself, these characterizations have a perverse way of putting me in mind of the many men and women I encounter in these age groups who are neither flaming, serene or sage.

To facilitate understanding of these new passages, Sheehy presents a graphic. Life, as she ultimately appears to perceive it, can be plotted and presented as if it were a board game. Thus, on her chart, the passages to what she calls the Age of Mastery and the Age of Integrity are designated by a bridge, arrows and a mountain path.

Though Sheehy defines midlife as the “metaphysical point where we recognize the end of unlimited promise and the fact that we cannot control many of the bad things that happen to us” (the italics are hers), the very notion of mapping one’s life across time implies that she IS EQUALLY CONVINCED believes equally that control is just out of reach. Clearly, this book will attract the many who crave the reassurance that comes from absolute order. And Sheehy is ever-ready to provide what she apparently believes most people seek: “theory, labels and explanations that would bring some order to the variousness of their experience.” To do so, she conducted hundreds of interviews with psychologists and people in midlife, read widely in the literature and initiated surveys of her own. The research is prodigious.

The problem is that in her schema, all of life, all of art, tend to be shaped by her own cookie-cutter. Her world is like the Steinberg drawing of New York City, where a looming 9th Avenue becomes My Theories.

For example, of the 1967 film “The Graduate,” she writes, “Much of the symbolism in this Mike Nichols film is a classic expression of Pulling Up Roots.” Later, Hillary Clinton’s speech on what the First Lady termed “the crisis of meaning” serves as “the first hint that Hillary Rodham Clinton was caught up in the crisis of middlescence.”

This is not a book to be read for style. In Sheehy’s idiom, the young Frank Sinatra is “a skinny crooner from Hoboken,” the Beatles are “a foursome of cocky young Liverpudlians,” while a 46-year-old auto-worker arriving for an interview “looked a little green around the gills, but eager to get some things off his chest.”

At her best, Sheehy clearly states ideas about life that have never before been as clearly stated. The notion of a Second Adulthood is one such idea. Another is the speculation that men and women, having similar personalities for the first 10 years of life, become respectively more aggressive and more nurturing, and finally take on each other’s characteristics, as men in mid-life and later life become more nurturing while women become more focused.

At her worst, she is glib, offering up New Age style answers that have been stated often and better by others. Are we to take seriously her notion that one of the things required by a woman who spends time visiting her husband, who has been hospitalized with prostate cancer, are “comedy tapes for the car?”

The books ends as Sheehy quotes the guru Deepak Chopra, who urges that everyone should learn “ . . . to accept your life . . . as a path of awakening.” With the facile optimism that characterizes this book in its entirety, she then concludes, “If every day is an awakening, you will never grow old. You will just keep growing.” But this promise is both cheap and empty. For as most people who have reached midlife can tell you, every day is not an awakening, nor would anyone have the psychic time or energy for this, not even in the most well-lived life.

Sheehy does not write as well or think as clearly as, for example, M. Scott Peck, who has the grace to allow that many of life’s essentials are unexplainable and unexaminable. Still, in her certainty, Sheehy has arrived at an overall view bound to have mass appeal, a view that, for better or worse, is one that, as F. Scott Fitzgerald once wrote in another context, “sounds like money.”

“New Passages,” read by Gail Sheehy, is available on audiocassette from Random House ($22.50; abridged).