PHILADELPHIA (AP) _ A knee transplant at the Hospital of the University of Pennsylvania was indicative of recent advances in bone surgery but no breakthrough, experts said Wednesday.

Dr. Richard Schmidt, who performed the operation on a 32-year-old New Jersey woman, had said the operation was ''the first total knee transplant I'm aware of.''

But Dr. Gary Friedlaender, professor and chairman of the Department of Orthopedics and Rehabilitation at Yale University, said along with other specialists Wednesday that the surgery was not the first of its kind.

''A lot of us have been doing these for years,'' said Dr. Steven Gitelis, director of the bone bank at Rush Presbyterian St. Luke's Hospital in Chicago.

''They maybe have taken a little bit bigger piece, which is good. I don't want to downplay what they're doing,'' said Dr. David Collon, orthopedic surgeon at Henry Ford Hospital in Detroit. But he added: ''It's not a giant step forward.''

The transplant was performed Sept. 30 on Susan Lazarchick of Absecon, N.J., who had a grapefruit-size tumor protruding from the front and back of her right shinbone.

Schmidt said the bone tumor was benign but had eroded her thighbone, strangled veins and arteries and left her unable to walk.

In a seven-hour operation, Schmidt and three others severed Ms. Lazarchick's leg above and below the knee and replaced it with a knee-joint from a Philadelphia teen-ager killed in a motorcycle accident.

Schmidt said Ms. Lazarchick should regain almost complete use of her leg.

Friedlaender said the first known knee transplant was performed by Erich Lexer, director of the Royal Surgical University Clinic and Polyclinic in Prussia. He published his results in 1908.

Friedlaender saiese procedures and that they must be able to donate tissues such as the bone, just as they do organs, in an altruistic sense, for the benefit of others,'' he said.