Rosemarie Maniscalco, the woman whose life physicians vainly attempted to maintain in order to save her 21-week fetus, became comatose Nov. 23 as a result of a stroke, the New York City medical examiner ruled yesterday.

Deputy Medical Examiner Dr. Milton Wald said the 27-year-old woman's condition was caused by "an explosive destructive hemorrhage that destroyed the left side of her brain." She died Tuesday.

Wald said he and Chief Medical Examiner Dr. Dominick Dimaio believe the stroke was a natural occurrence, and was not caused by an act of violence.

Maniscalco had a week blood vessel in her brain that "was there since she was born . . . like a time bomb" that "apparently doesn't kick off until 20 or 30," Wald said. Such a condition is not uncommon in persons in their middle 20s, he said.

The Brooklyn, N.Y., district attorney's office is investigating allegations that Maniscalco was at one time beaten by her husband, John. He has repeatedly denied the allegations, and physicians treating his wife said they saw no signs that she had been beaten.

Hardie Mintzer, a spokesman for District Attorney Eugene Gold, said yesterday that the "investigation is continuing" despite the medical examiner's report.

Asked why the investigation, being conducted by the prosecutor's homicide office, would continue in light of a finding that the woman died of natural causes, Mintzer said, "No comment."

Joseph Derrico Jr., an attorney representing John Maniscalco, said Gold "has to present the doctor's report to the grand jury." He expressed confidence that the grand jury will drop the matter.

Physicians at Victory Memorial Hospital in Brooklyn worked for 13 days to sustain Maniscalco, hoping to keep her alive and allow her fetus to develop sufficiently to be delivered.