NOW AND THEN: From Coney Island to Here.<i> By Joseph Heller</i> .<i> Alfred A. Knopf: 240 pp., $24</i>

Any author who coined a word that embodies the existential dilemma of our world, who wrote a first novel that changed the way we regard one of our most hallowed national experiences and who anticipated and shaped the counterculture with his absurdist and iconoclastic sense of humor has surely earned the right to reminisce about his life and work. Readers may then pick up Joseph Heller’s literary memoir, “Now and Then,” with real enthusiasm and anticipation.

As it turns out, there is a catch.

Heller, who is as sly and mischievous as his novels, is not ready to share with his readers what they really want to know: the wartime experiences that prompted him to write “Catch-22.” Rather, as Heller allows us to understand, he is saving the story of “Catch-22” for a second memoir; the current book is really a sentimental celebration of his childhood in the neighborhood of Brooklyn called Coney Island.

A few intriguing asides about “Catch-22” can be culled from the pages of “Now and Then,” which makes at least a few touch-and-go landings in the landscape of Heller’s exploits as a combat pilot in World War II. Heller recalls a young pilot with “patient genius for building and fixing things” and a gift for surviving close calls in combat who was the oblique inspiration for the slightly mad bomber pilot named Orr, and he reveals how a conflation of a wounded gunner, whom Heller actually nursed, and a dying gunner, whom Heller only heard about, became the haunted and haunting figure of Snowden. Some memorable bits of dialogue from “Catch-22”--”The bombardier doesn’t answer!” “I’m the bombardier”--were actually uttered by Heller and his comrades in air combat over Europe.

More attention is paid, however, to Heller’s experiences before and after the war. “Now and Then” is Heller’s earnest contribution to the vast literature that has been inspired by both the idea and the reality of Brooklyn, thus earning it a place somewhere between books like Alfred Kazin’s “Walker in the City” and Betty Smith’s “A Tree Grows in Brooklyn.” He conjures the same magic that others have noticed in those mean streets, and he sings the familiar song of Nathan’s hot dogs, the tunnel of love at Luna Park and Saturday afternoon matinees with “a Mickey Mouse or Betty Boop cartoon or travelogue thrown in.” Indeed, his vision of Brooklyn in the ‘30s and ‘40s is purely rhapsodic.

“Our street and neighborhood felt safe, insular, and secure,” recalls Heller, who insists that there was “just about no fear of violence . . . and practically no crime” in Coney Island.

Tellingly, the life-threatening and life-changing incident that Heller describes with the greatest passion is not an experience of air combat in World War II but a daring childhood swim to a bell buoy in the waters off Coney Island. The faintly surrealistic sight of the amusement park growing ever smaller as he swam to sea stirred his “haunted imagination” to real terror--and still does. “A mere revisit in memory to that Lilliputian picture is sufficient to chill,” confesses Heller. “Today, I wouldn’t try that swim for a million dollars, tax free.”

From Coney Island, young Joey ventured into Manhattan, where he worked as a Western Union delivery boy, and then to Virginia, where he served a short stint as a somewhat baffled defense worker in a Navy blacksmith shop that made anchor chains: “I still don’t know how these links of chain were made,” he confesses, “and have stopped wondering.” And then he drops one of the occasional enigmatic asides that somehow reveal the workings of his mind: “Today I worry instead about tiny jewelry chains,” a comment revealing an endearing if eccentric curiosity about the world around him, “how in the world the minuscule filaments are assembled into those flexible segments.” The very fact that Heller frets over such things without bothering to find out how either chain is made suggests that he spends more time in the realm of memory and imagination than in the real world.

A few passages are devoted to Heller’s sojourns in Southern California, where he trained as a bombardier during World War II and where he returned after the war to attend USC on the GI Bill. Heller pauses to note that he “sneered at things like college spirit” and sold the Rose Bowl tickets he received as an undergraduate so he could spend the proceeds on his real passions: the races at Santa Anita and Hollywood Park.

Only rarely is Heller willing to reveal something truly intimate about himself. The ghost of his father, who died when Heller was young, stalks the pages of “Now and Then,” but he seems to be safely confined to the author’s dream life and his musings on a psychoanalyst’s couch. Perhaps the most surprising and gratifying confession is one in this book that touches on the war experiences of “Catch-22”: Heller, who flew 60 combat missions in World War II, is a nervous flyer and “inconspicuously” crosses the fingers of both hands on takeoffs and landings.

But aside from this, most of his moments of self-revelation are mild and unremarkable. “In my book ‘Closing Time,’ I say of a character, Yossarian, that he couldn’t learn to make a bed and would sooner starve than cook,” writes Heller. “That is autobiography.” But in that book Heller sought refuge in comic irony, and he knows it: “I am walking proof of at least part of Freud’s theories of repression,” he confesses in “Now and Then,” “and perhaps, in writing this way here and in other things I’ve published, of denial and sublimation, too.” To which the reader might respond: Now that’s autobiography.

Moments of genuine charm are woven into Heller’s memoir, and the book will help the appreciative reader of his novels to understand something more of the man who wrote them. But “Now and Then” gives the preliminaries for a literary autobiography, and the book only whets the reader’s appetite for the memories and revelations that Heller has yet to share. Let us hope that he does not hold back the main course too much longer. He deserves to finish the half-memoir that he has written, and those of us who hold him and his work in the highest esteem deserve the opportunity to read it.