LOS ANGELES (AP) _ A professor convicted of killing and dismembering a teen-age prostitute with a chain saw was sentenced Friday to 25 years to life in prison by a judge who said the educator was ''a Dr. Jekyll and Mr. Hyde.''

Max Bernard Franc, 58, whose secret life as a homosexual voyeur was disclosed during his trial, coughed slightly but remained impassive as Superior Court Judge John Reid imposed the maximum sentence.

Reid described the murder of Tracy Leroy Nute, 18, and the dismemberment of his body with a chain saw as ''hideous, cruel and callous.''

Franc was accused of shooting Nute, a runaway from Kansas City, Mo., chopping up the body and distributing it across 200 miles of California. Franc said a transient named Terry Adams committed the crime. But Adams was never found.

''Dr. Franc, the one thing that becomes very clear to me is you are two different people,'' said the judge. ''You're the scholar to your colleagues. Your students talk about you as if you were the second coming as a teacher. But none of them talk about what was going on in the Hollywood area of your life.''

Franc, who taught at Fresno State University until his arrest last August, had maintained an apartment in West Hollywood, some 200 miles away, where he paid young men to pose for nude photographs, his attorney has said.

''An analogy has to be drawn to Dr. Jekyll and Mr. Hyde,'' said the judge.

He imposed the sentence after Franc's sister, Carol Waiters, a social worker from Philadelphia, made an impassioned plea for her brother, describing him as a brilliant, bilingual teacher who inspired his students.

''I ask, I beg of you, Judge Reid, do not let this mind go to waste in prison,'' Mrs. Waiters said in a trembling voice.

''He has so much to offer,'' she said. ''To shut him away and snuff out his creativity and productivity would be a terrible waste to society.''

Reid said he hoped Franc would use the time in prison to help uneducated inmates improve themselves.

''I hope you do something beneficial with the rest of your life,'' he said. ''I think it's a shame it had to come to this. But these are your acts, no one else's acts.''

Franc, a native of DePere, Wis., was arrested after a chain saw he had rented was returned with bits of flesh and blood in it.

''Even if the only thing you did was watch someone else kill Terry Nute, what type of person could go and rent a chain saw knowing it would be used to cut up a body?'' the judge asked Franc. ''There's no question that's exactly what you did.''

Deputy Public Defender Mark Kaiserman lost a bid for a new trial and reduction of the first-degree murder conviction. The judge said he felt the jury's verdict was proper even if Franc had only aided and abetted in the murder. He conceded that what actually happened was never clear and he could not conclude positively that Franc pulled the trigger to kill Nute.

Deputy District Attorney Sterling Norris said Franc ''ought to feel lucky that he doesn't go to the gas chamber'' because special circumstances were not involved in the case.

He said the pleas for leniency based on Franc's status as a college professor ''smacks to me of class distinction.''

Kaiserman said Franc will appeal his conviction.