The prosecution began its efforts yesterday to convince a Montgomery County district court judge that 18-year-old Sherry Windt, the Bethesda girl charged with the fatal stabbing of her mother two years ago, was sane at the time the slaying occurred.

Windt's attorney has contended that his client was legally insane on Oct. 16, 1975, the night her mother, Marjorie Windt, was stabbed to death in the bedroom of the Windt apartment.

Judge Douglas H. Moore Jr. must eventually determine whether Sherry Windt was in fact insane at the time and whether she is currently competent to stand trial. A ruling by Judge Moore that Windt was insane at the time would result in her acquittal by reason of insanity.

There is little likelihood that Windt would be immediately released, however, in the event of such an acquittal. The judge would then have to determine whether she was a danger to herself or the community, and while that was under consideration she would most likely remain in the care of the court.

At the hearing in juvenile court yesterday. Windt sat upright and stiff four hours, as two prosecution psychiatrists attempted to contradict her attorney's insanity defense of the murder charge.

In previous hearings on another legal question, one psychiatrist had described Windt as a deeply disturbed young woman with three distinct personalities who retreated into "dissociates states," where she lost all awareness of the world around her.

She was in just such a state, the psychiatrist testified at the time, on the night her mother was killed. Most probably she did not consciously realize what was happening, he testified.

Yesterday two psychiatrists called by the prosecution said they doubted that theory.

Dr. David Tractenberg, a Bethesda psychiatrist who saw Windt as a patient in late 1974 and whose associate also treated her in early 1975, testified that she was suffering from a mental disorder that consisted mainly of difficulty in making the transition from a child to an adult.

he said that, during his interviews with her, he noted no "dissociative reactions," moments when Windt would lose contract with reality.

Dr. Brian Crowley, another Bethesda psychiatrist who examined Windt in 1976 and again last month, also said he did not believe she could have suffered from these dissociative states in October 1975.

Crowley also testified that he does not believe Windt met the legal requirements for insanity on the night of the crime.

On cross-examination, Crowley said that his conclusion rested partially on the fact that he found no history of dissociative reactions on Windt's part. Windt's attorney, Walter Madden, then called one of Windt's former teachers and a cousin who testified to occasions when they had seen Windt suddenly tune out from her surroundings and tare off into space.

Windt, who has been receiving treatment in the Baltimore-based Institute of Psychiatry and Human Behavior since last year, was to return to court today. A ruling in the matter is not expected for several weeks, however.