Reflections in the Fragments : THE SECRET DEFECTOR, <i> By Clancy Sigal (Aaron Asher Books/HarperCollins Publishers: $22; 274 pp.)</i>

Where does reality end and imagination begin? That’s a question that seems particularly appropriate to ask when it comes to Clancy Sigal, whose writing has always danced the fine line between memoir and fiction in a uniquely elusive way.

From “Weekend in Dinlock” and “Going Away,” his two autobiographical novels of the early 1960s, to “Zone of the Interior,” a 1976 roman a clef about his LSD-enhanced descent toward schizophrenia under the tutelage of R. D. Laing, Sigal has consistently used the raw content of his life as the substance of his work, meditating not only on his own experiences but also on the very process by which they are transformed--the writer’s constant, messy struggle to reimagine himself and the world in which he lives.

Sigal’s fourth book, “The Secret Defector,” continues in this vein of autobiography filtered through the veneer of fiction. Called a novel, it covers the last 30 or so years of its author’s life--beginning with his expatriation from the United States to England in the late 1950s, and ending with his return to Los Angeles, on the eve of “a war starting in the Persian Gulf.”

As a result, perhaps, of its scope, “The Secret Defector” rehashes a substantial amount of material from Sigal’s first three books, even bringing back certain figures and situations that have appeared in his fiction before. Again, for instance, the Sigal character--known as Gus Black in this incarnation--spends time living with a female writer (based on Doris Lessing, with whom he had a tumultuous relationship during his first few years in Britain), who is using their love life to fuel a novel called “Loose Leaves From a Random Life.” Again, he spends time in a Yorkshire mining village, seeing how the workers live.

And again he seeks out the unorthodox treatments of Dr. Willie Last, the Laing-like psychotherapist from “Zone of the Interior,” when reality becomes too difficult for him to bear.

But while this kind of literary deja vu may be problematic for readers familiar with Sigal’s previous efforts, it works within the context of “The Secret Defector” because the entire novel reads as a recapitulation, as the testimony of a writer feeling the shadow of his own mortality and engaging in the necessary act of summing up. In that sense, Sigal’s other books--and the encounters they describe--are simply pieces of the fabric from which this new volume is made, a synthesis that becomes most clear when the narrative of “The Secret Defector” moves beyond the events and endeavors about which Sigal has already written and into territory that is wholly new.

Thus, although it encompasses them, “The Secret Defector” is not a tale of coal miners, nor of cosmic soul-searching with an acid guru. It’s the story of a life spent in the tenuous middle ground between the fringes and the mainstream. Like Sigal, Gus Black is a Marxist who escapes the specter of McCarthyism for the sanctuary of the British New Left, only to become embroiled in the chaos and confusion of the 1960s and 1970s, in the clash between politics and fashion, between responsibility and freedom, and his own internal conflict over how, and whether, he belongs.

A writer who can’t write, a radical who becomes a suburban squire in spite of his ideals, an American self-exiled in a country that will never let him forget where he is from, Gus is a perfect mirror for the fragmented times in which he finds himself, a man looking for continuity in a world that has forgotten such a thing exists. Cut adrift, he must invent himself as he goes along, looking for the pieces of a personal mythology wherever he may find them, from the movie references that flavor this novel like fine spices to the central metaphor of the “secret defector” that unifies the book by pinning a label upon Gus’ ever-vacillating heart.

Heart, after all, is what “The Secret Defector” is really all about. It is a passionate novel, full of love affairs and political confrontations that resound all the more powerfully because of Gus’ fear that, despite his involvement, he is somehow emotionally deficient--”faithless,” a defector, who is “always alone . . . even in . . . marriage.” Sigal’s decision to take the novel in this direction is a dangerous one, given his connection with the character, but it’s a decision that pays off because of his scrupulous willingness to expose himself all the way, a willingness that elevates his story to the level of art.

For the idea of defection is universal; it is embedded within every one of us who has lived long enough to grow away from the people and the things we love. And by allowing Gus to be unflinching in his self-reflection--about the women in his life, with whom he feels like an impostor; about the political issues which, as he gets older, seem less and less clear-cut; and about his younger self, “a socialist while I was a survivor,” who, by the novel’s end, is still “demand(ing) . . . loyalty oath(s)”--Sigal makes of him far more than just an alter ego. He gives him texture, and enables him to come alive.