Henri Van der Vreken, the chilly and condescending house manager for the late Dr. Herman Tarnower, took the stand today and told the jury in the Jean Harris murder trial that he had seen Harris fleeing the doctor's home the night the doctor was shot to death. And, he said, when Harris returned to the scene she stood apart from those aiding the dying doctor, offering no help, doing "nothing."

But the credibility of the prosecution witness suffered a sharp blow later when, under cross-examination from taunting and accusatory defense attorney Joel Aurnou, Van der Vreken lost his composure and blurted out feelings about Harris that showed he was in no way an objective observer.

"I don't remember many things because I was extremely shocked by what happened," the Belgian servant said, in his heavy French accent, growing more rattled by the attorney's attacks. "You have to go through something like that to know; I wouldn't want anybody to go through that. . . ."

"Then you have strong feeling . . . ," interrupted Aurnou, aggressively, trying to get Van der Vreken to admit he had made up his mind about Harris' guilt.

"It's not a question of feelings at that time," said Van der Vreken, emotion choking his speech. "You just don't have any feelings at all. . . ." He struggled for words. "When you find yourself in such . . . an immoral murder. . . ."

Former headmistress of the Madeira School in McLean, Va., Harris, 57, has been charged with second-degree murder in the shooting death of her lover, Tarnower, in the bedroom of his Harrison, N.Y., home in March. The prosecution, noting that Tarnower, a celebrity because of his best-selling Scarsdale diet, had been seeing another woman, claims Harris shot Tarnower "intentionally" in a jealous rage. The defense insists that Harris drove from her home in Virginia to the doctor's to commit suicide, that the shooting was simply a "tragic accident."

The defense position, however, has been battered considerably in past weeks by a string of prosecution witnesses, including a doctor who last week testified that Tarnower had been shot four times, including once in the back.

Today, the 16th day of the testimony, Henri Van der Vreken, outlined events of the day Tarnower was shot.

Tarnower, Van der Vreken told the jury, had begun his day in the company of Harris' rival, the younger Lynne Tryforos. He had breakfasted with Tryforos, left the house early to go to his office, returned home briefly in the middle of the day on an errand regarding wine and had come home at about 5:30 p.m. That evening, he had given a small dinner party for a niece and Tryforos, after which he had gone early to bed. Van der Vreken retired to the guest bedroom shortly thereafter. The next thing he knew, Van der Vreken said, his wife was awakening him.

"She was very much hysterical," he said, over the objections of the defense.

". . . I tried to get some help. . . I went to the kitchen and tried to call the police . . . then I went outside and went around the block and when I went in the driveway I saw a car leaving the house . . . a blue Chrysler with a white vinyl top. . . I said to myself, 'This is the car of Mrs. Harris. . . .'"

Under direct examination from Assistant District Attorney George Bolen, Van der Vreken said he returned to the house, called neighbors "to give a description of the car and tell them to stop that car one way or the other." He also described coming upon mortally wounded Tarnower and he recalled Harris' response at the time.

"What did you do see Mrs. Harris do with respect to helping the doctor?" asked Bolen.

"Nothing," said Van der Vreken.

Van der Vreken also named a number of neighbors of the Tarnower residence, an apparent attempt by the prosecution to establish that Harris need not have traveled as far as she did from the house if she was truly looking for a phone. (The defense has maintained that Harris, who was seen leaving the house, was not fleeing the scene, but leaving to call for help because the doctor's phones were out of order.)

Under cross-examination, however, the prosecution suffered. Sarcastic and biting, Aurnou wasted no time trying to shake the witness.

Van der Vreken had said that Harris stood by idly and had done nothing after the doctor was shot.

"Up to that point, what had you done to help the doctor?" Aurnou asked.

"What can I do to help the doctor?" shot back Van der Vreken, irritably.

"I don't know," said Aurnou. "But Mr. Bolen had asked you what Mrs. Harris had done after the doctor had been shot. I thought you might have had a suggestion."