He can't run, but 29-year-old Floyd Hartley of Baltimore can walk painlessly again following the implantation of two experimental artificial knees designed to last much longer than the prosthetic devices of the past.

Baltimore developers of the new knee say it is the first to allow the patient's own bone cells to grow into the device itself, producing an unusual union which could be stronger and more stable.

Dr. David Hungerford, who developed and tested the artificial knee with colleagues at Johns Hopkins Medical Institutions and Good Samaritan Hospital, considers the initial success in using this combination approach to be "just the tip of the iceberg."

He predicts more widespread use of the process in other parts of the body, from artificial teeth to other joints. Doctors already have made limited applications of the process in hip replacements, and the Baltimore team is in the process of developing their own hip device as well.

A paper outlining two years of experience with the knee replacement was presented yesterday at the annual meeting of the American Academy of Orthopedic Surgeons in New Orleans.

The device, called the "porous coated anatomic total knee," is coated with chrome cobalt beads, providing a surface that encourages the patient's bone cells to grow into the artificial joint. Hartley, a victim of rheumatoid arthritis who underwent surgery twice in 1980, is one of 22 patients--followed for an average of 15 months--in whom X-rays documented that this "biological in-growth" actually took place.

In the past, the commonly used technique has involved cementing an artificial knee into place, which also loosens over the years and eventually must be replaced. About 40,000 Americans annually undergo surgery to replace knees weakened by accident and disease--mostly from arthritis and, less frequently, football injuries.

Hungerford estimates that more than half would be candidates for the porous, artificial cementless knee. He believes that, theoretically at least, the cementless knee would "last indefinitely"--at least several times longer than existing prostheses--but cautions that it has not been studied long enough to know just what the span would be.

The metal-and-plastic device is installed by drilling holes in the lower end of the thigh bone and the upper portion of the shin bone. The original knee joint is removed and the artificial knee is attached to the bones with pegs that are fitted into the holes and pressed tightly into place. The false knee is expected to grow stronger as the patient's own bone cells get a grip on the new joint.

"This is particularly important for young people," says Hungerford. "They're more active and put greater stress on their knees. And their longer lifespan means they would have to have a cemented knee replaced more often."

At present, the cementless device is available only for experimentation, and still awaits final Food and Drug Administration approval, Hungerford said by telephone. FDA officials attending the meeting were unavailable for comment.

It is also manufactured commercially for conventional use with cement for patients who have lost too much bone or whose bones have become too worn down for the experimental technique.

From the patient's perspective, the new knees work "just beautifully," according to Hartley, who earlier underwent surgery to have artificial hips cemented in place. He says he now gets around easily in his job as a computer aide at the Social Security Administration.

The former athlete, who was afflicted with arthritis the summer after high school as he was contemplating a professional baseball career, can't play sports himself. But he's happy to be able to stand on the sidelines as a volunteer coach for kids.