The star defense witness in the Jean Harris murder trial testified today that blood patterns found at the estate of Dr. Herman Tarnower indicated that Harris and Tarnower had been involved in a struggle in the doctor's bedroom moments before he was killed.

The witness -- an internationally known professor of criminology who has written a federally funded manual on bloodstains -- told the jury that blood stains found between the twin beds in the Tarnower bedroom were not consistent with drops merely dripping from a bleeding man.

"There was some sort of activity or movement over the carpet, or perhaps some gushing from an artery," the witness, Prof. Herbert Leon MacDonell, said.

"Would it be consistent with a struggle?" asked defense attorney Joel Aurnou.

"It would be consistent with what I consider a struggle, two people moving around, or more than one person in contact. . . ," the witness said.

Former headmistress of the Madeira School in McLean, Va., Harris has been on trial for three months now, charged with second degree murder in the shooting death of her lover in the bedroom of his home. The defense position, throughout the trial, has been that the shooting was accidental, and that the four wounds Tarnower sustained -- including one to his back -- occurred only when a "struggle" took place.

Today, the defense continued to battle for that position, bringing to the stand for the second day MacDonell, a criminologist whose work in the Black Panther murder trial in Chicago was instrumental in indicting 35 policemen as well as a local district attorney.

A greybearded, wry gentleman, whose expert-witness fee begins at $800 a day, MacDonell spoke in impressive scientific detail throughout the day -- detail that caused at least one member of the jury to doze repeatedly. But his arcane expertise made him an unshakeable witness. Going against him, with his level of expertise, was like going against the deity. The deity did, in fact, enter into the testimony at one point, parenthetically, when MacDonell used the courtroom Bible to illustrate a ballistics point. ("I hope this isn't sacrilegious," he said.)

Expert in ballistics and fingerprints as well as bloodstains, MacDonell today reiterated a point he had made Monday -- that the wound Tarnower sustained through his right hand was not a defense wound, inflicted as the doctor held his hand in front of his body to defend himself, but a wound that could have been sustained when the doctor held his hand over the muzzle of Harris' gun, as she held that gun to her own head.

Under questioning from defense attorney Joel Aurnou, MacDonell said that blood patterns in the bedroom, as well as on the doctor's body and clothing, indicated that he had not been shot as he held his hand in front of him to protect himself.

". . . that would have caused a tremendous amount of spattering in the direction of the shot . . . most parts of his anatomy would be covered with blood, his face, also his shirt, whatever clothing he was wearing."

The defense attorney held up a pajama top the doctor had been wearing at the time of his death for the expert's inspection.

"I don't see any evidence of such spattering," said the witness, examining the top carefully. "Of course the sleeve is stained in places . . . there could be spattering under the stains . . . but I do not see any evidence of spattering in the unstained areas."

There was no explicit testimony regarding the wounds the doctor sustained to his back, arm, and chest. But the defense attorney did set the legal groundwork for the wound to the chest -- an extremely shallow wound, which the prosecution says resulted after a bullet smashed through the doctor's hand into his chest -- by quizzing MacDonell on ammunition.

Could there be variance, even among the same type of ammunition, in the distance a bullet would travel, Aurnou asked.

"Yes," said the witness.