SUSAN SONTAG IS best known as a critic who has insistently reminded American readers that a vast contemporary world of thought and imagination continues to evolve on the other side of the Atlantic. Whether she is discussing books or movies or philosophical concepts, Sontag finds her apt illustrations, if not her central theme, in the European tradition, especially in France. In this she bears a resemblance to Matthew Arnold whose love affair with Europe gave to his literary and cultural criticism a breadth of reference otherwise lacking in early Victorian England. Like Arnold, too, Sontag holds firmly her belief in the saving power of reason ("I, for one, do not doubt that the sane view of the world is the true one"), but she never blinds herself to sometimes dazzling light cast by the experience of the absurb. And so her collections of criticl essays map the modern terrain from Camus to Camp, from Simone Weil's tormented life to Bergman's tortured and torturing characters.

It is in her criticism, as well, that we find a key to her fiction. An essay on "The Pornographic Imagination" leads Sontag to explore the diversities of prose narrative; in place of a simplified notion of "realism," which would correspond roughly to representationalism in art, she offers as the writer's-and the critic's-principal focus "the complexities of consciousness itself, as the medium through which a world exists at all and is constituted." With this more sophisticated point of view, "exploring ideas" becomes "as authentic an aim of prose fiction" as "dramatic tension or three-dimensionality in the rendering of personal and social relations." Traditional character development gives way to the depiction of "extreme states of human feeling and consciousness," where the links with concrete individuals may be no more than contingent.

In the essays, Sontag develops these points for a specific purpose-to argue that certian kinds of pornography, as the expression of just such an "extreme state" of consciousness, may be said to achieve the quality of art. But the same ideas apply equally well to her own-definitely non-pornographic-fictions. All of the stories in this collection, with varying degrees of success, probe relentlessly at the thin membrane of our modern consciousness. Even the two "travel accounts" that bracket the collection, "Project for a Trip to China" and the splendidly lyrical finale, "Unguided Tour," have much more to do with the inner landscape of memory and imagination than with external geography.

But place is not neglected etiher, at least insofar as it reflects the vagaries of language and expression. Two stories, "Debriefing" and "Baby", rely for their effect on their locales, respectively New York City and Los Angeles, which are conveyed not so much by geographical referents as by two quite distinct forms of upper-middle-class talk. "Debriefing" works better, partly because it makes its point about anomie and alienation with considerably more economy, but also because it captures the fortuitous and often absurd intersections of urban life without surrendering a stubborn note of compassion. Just before the story's deliberate anticlimax, the narrator, who tries to hold the whole city together in her head, sums up her life's work in splendidly staccato New York fashion: "I exhort, I interfere. I'm impatient. For God's sake, it isn't that hard to live."

In its own way, "Baby" is no less accomplished as a tour de force of contemporary monologue; the hip parents spew out their cliches before the silent, psychiatric oracle. Obsequious and truculent in turn, they recount the history of the angel-devil they have reared and finally destroyed.Events are conflated, statements contradicted, blame shifted and accepted-all ina medley of cliches:

"Maybe Baby ought to see a doctor, too.

Baby's handwriting is very strange.Should we bring you a sample?

Just say the word.

Baby keeps a journal. Under lock and key, mind you.

We wouldn't dream of it. That would be one hell of a fast way to lose his confidence, wouldn't it doctor?"

After 40 pages, the reader gets swamped by this torrent of banality, and the final two-page litany of petitions ("Tell him he's free. Tell him he can't leave us alone. Tell him. . .") fails to invest the story with desired sense of tragic pathos.

Another 40-pager, "Old Complaints Revisited" suffers from a similar surfeit of explanation, this time presented in epistolary form. But it does succeed in conveying, partly by its self-consciously neutral and anonymous tone, the general pschological and moral dilemma of belonging to a group one is alienated from, whether it be a political party, a religious sect, or even a distinct ethnic group.

What is striking about these five stories and the other three, taken as a group, is the wide range of literary forms Sontag has chosen to exploit in presenting her various "extreme states of human feeling and consciousness." "The Dummy," for instance, her earliest effort, borrows a science-fiction prop-the perfect mechanical replica-to explore the desire to escape from one's role in life and yet continue to observe it. With a characteristic ironic twist, the dummy and his replica in turn prove to be much better at being human than their inventor, thus leaving the little suitably ambiguous.

"American Spirits" parodies our national ambivalence toward domestic virtue and sexual anarchy by using the devices of the morality play in their jazzed-up cinematic version. The cast includes a heroine named Laura Flatface, a villain known only as Mr. Obscenity and Laura's two all-American husbands who seal the triumph of virtue at her funeral with a manly embrace. Politics, literature, myths and media-all get their comeuppance in this sly parable about America's image of itself. And, to complete the set of literary transpositions, "Dr. Jekyll" moves Stevenson's split personality to New york where an apparently omniscient mind controller named Utterson programs and deprograms willing disciples at an Oyster Bay estate. In the end, Jekyll's impotent rage against Utterson is transferred to his seedy dopelganger, and the humane doctor ends up in jail for attempted murder.

Whatever strategy she chooses in her quest for images of modern consciousness, Sontag deploys it with a sure sense of artistic form and ironic juxtaposition. Occasionally, however, her talent for appropriating and parodying the literary tradition overwhelms her own content and leaves the reader with the uneasy feeling that wit has triumphed over substance. But at her best, and this includes large chunks of even the less successful stories, Sontag illuminates our contemporary situation with the peculiar radiance that comes from the fusion of wide learning, precise thinking and deep feeling. Suddenly we see our own face in the mirror and hear our own voice with a shock of recognition all the greater for the restraint with which the revelation is made.