The bullet wound in the hand of Dr. Herman Tarnower, like other facets of Jean Harris' murder trial, has been a matter of contention.

The prosecution -- arguing Harris intentionally shot her lover -- claims the wound was sustained when the Scarsdale diet doctor held up his hand to ward off Harris' attack as she fired a round that passed through his hand and into his chest. The fact that the wound to the doctor's chest was unusually shallow -- barely an inch deep -- supports that theory, prosecution witnesses have claimed.

The defense has a different version of what happened. It claims that Harris put her .32-caliber gun to her own head. The defense says her lover seized her hand and pulled it away as the gun went off -- and that the bullet tore through the doctor's hand and out the glass door of his bedroom.

Today, the defense brought out what may be its most important witness -- an intentionally known forensic expert who testified at the black Panthers trial in Chicago and was called in on the Robert F. Kennedy assassination -- to support that view. Based on bloodstains and bullet holes at the scene, Prof. Herbert Leon MacDonell said that Tarnower could indeed have been wounded wrestling the gun from Harris.

"Is the high-impact velocity splatter you found consistent with the possibility of a .32-caliber gun fired through a human hand held over the muzzle of a gun?" asked defense attorney Joel Aurnou.

"Yes," said the grey-bearded professor.

But there was no testimony today about what appears to be some of the most damaging evidence against Harris: the three additional bullet wounds in Tarnower's body, including one in the back.

Former headmistress of the Madeira School in McLean, Va., Harris is on trial on charges of second-degree murder in the shooting death of her lover, author of the best-seller on the Scarsdale diet. The prosecution charges the shooting was intentional, the act of a jealous, aging woman. The defense calls the shooting a "tragic accident." Tarnower was shot, the defense claims, after Harris entered his bedroom to commit suicide and, in the struggle that followed, the gun went off -- four times.

Today, the defense continued to support that position with MacDonell, a professor of criminology at Corning Community College in Corning, N.Y., who lectures around the world and wrote the book -- literally -- on bloodstains, a tome on "the properties of blood in motion," the research for which was funded by the Justice Department.

It took an hour for the defense to elicit all of his credentials. Most impressive, perhaps, was his work in the Black Panther murder trial in Chicago, which dealth with a 1969 police raid on a Panther apartment that left two Panthers dead and several charged with murder. MacDonald told the jury today that he was instrumental in the Panthers' defense, proving that police had fired first.

That sort of dramatic turnabout evidence, will be forthcoming from MacDonell in this trial. There was some indication of the weight his testimony might have, as he held forth on bullet trajectories and angles, and the properties of lead, glass and blood.

"A large quantity of blood could be flying several feet, while a small quantity does not have sufficient energy to travel even that far," he told the jury. "It could be equated to hurling a glass ashtray and a handful of sand just wouldn't have the same density to travel as far, though the content, silicon dioxide, is basically the same."

He received more jury attention when he went into one of the ways he and his fellow forensic scientists had tested "high-velocity blood spattering" -- by anesthetizing animals, shaving parts of their bodies and shooting them in that area.

"We took animals which were being destroyed . . . dying, old animals which were being put to sleep anyway . . . and we shot several of them and analyzed the kind of splatter that would result. . . .It was a practical application of a rather unpleasant experiment. . . . I do remember the loss of several frogs on campus as the result of high-velocity gunshots. . . ."