As this huge, sprawling novel opens, Sister Angela Flynn, 33 years old and covered in her own blood, is being rushed to a hospital from the St. Rose of Lima Convent in Cambridgeport, Minn.

A few hours before, she had delivered herself of a son without assistance, severed the umbilical cord with her teeth, smothered the newborn child, hidden it in a wastebasket and concealed the wastebasket behind a bookcase -- then lapsed into amnesia.

But not all of this will be apparent until later, when the novel has slowed down a bit. Sister Angela did not collapse until she tried to clean up the convent (a place normally "all clean and plastic-wrapped") and discovered that she had shed more blood than she could cope with.

From this summary, one might conclude that Catherine Breslin's first novel is sensational in style -- and in a sense it is, as sensational as was an actual news story some years ago -- although Breslin, a former reporter, assures readers that "this novel is a work of fiction, of imagination." But considering her subject matter, the treatment is quite sober and restrained once she gets past the initial, unavoidable blood and guts.

In the long run (and the book does run too long by perhaps 10 percent), Breslin's subject is not so much nuns who have and dispose of babies but how such an incident affects people -- above all the person to whom it happens, but also the members of her religious community and the church at large, family, friends, doctors, attorneys pro and con, average citizens and the press. Angela's baby is like a rock dropped into an apparently quiet pond, and for 600-odd pages one watches the denizens scrambling to cope with the incident.

At the cneter of the scramble, providing a balance and contrast to Sister Angela, is Meg Gavin, a 36-year-old reporter who feels that her career is going nowhere at a St. Paul newspaper, sees in the story the possiblity of attracting attention that will get her a better job and finally becomes involved in it at a level beyond the limits of professionalism.

Also torn between professionalism and sympathy is Lt. Tim Vance, who first guesses but cannot prove the central fact of the case: that Sister Angela has two personalities, one of whom went out and got pregnant, leaving the other to cope with a pregnacy she had not expected and did not understand. Equaly well drawn, though in less detail, are a host of minor characters, including a defense attorney who despairs of getting his client to relate to the show-biz aspects of a trial; members of a grand jury who let prurient interest blur the single-minded pursuit of truth and justice, and Angela's fellow nuns, who display an interesting array of hangups under their veneer of dedication but emerge finally as people struggling to be good in their own way.

Angela herself, behind the modern dress, the pregnancy and the spasmodic violence of the book's opening, turns out to be a quiet, somewhat old-fashioned person, puzzled about what has happened to her, and finally falling back on lies (which, of course, she believes) in her effort to understand and explain it all. She nearly wins herself a prison sentence because she cannot accept her attorney's approach ("When it came to . . . female witnesses in a sex-oriented case -- he knew that the truth was not nearly as good an armor as three wet handkerchiefs").

In her insistence on vindication rather than simple acquittal, in her pitiful efforts to believe that what obviously did happen could not possibly have happened, and above all in the time-honored ecclesiastical mannerisms to which she retreats when reality becomes too hot, Sister Angela begins, after a while, to look like a study in self-righteousness, a sin less human and forgivable than that by which she became pregnant.

At the time when some forms of pop or cult religion seem to be setting themselves up as enemies of civilization as we know it, this could be a very unsympathetic position to be in -- but Breslin understands her subject, and in sharing her understanding, she enlarges the limits of a reader's awareness. "Unholy Child" is a flawed book, and one that could have benefited from judicious trimming. But for those who are not revolted by its basic subject, its best moments make the occasional bouts of distaste or tedium worth enduring.