Prevention of paralysis after spinal cord damage -- one of medical science's dreams -- may be a step closer.

A New York University scientist says he has reversed severe spinal cord damage and prevented permanent paralysis in cats by injecting a drug as much as seven weeks after injury.

The achievement, Dr. N. Eric Naftchi says in the current issue of the journal Science, "introduces a new approach to amelioration and restoration of function" after spine injuries.

Thousands of persons are paralyzed every year after spinal cord damage in car and motorcycle crashes, gunshot wounds, diving accidents and other mishaps.

Two years ago, two Army scientists here -- Drs. Alan Faden and John Holaday -- created spinal cord injuries in anesthetized cats, then successfully prevented paralysis in some by injections of naloxone, a drug widely used to counteract heroin and morphine overdoses.

Since then, their work has been confirmed by other scientists, and Faden and Holaday have used another drug, TRH (thyrotropin-releasing hormone), with even better results. These drugs have to be used within the first few hours of injury, however, to have any hope of preventing paralysis.

Naftchi, too, created injuries in cats, but then injected them with clonidine, a drug that lowers blood pressure. It restored at least some nerve cell activity in 17 cats, he reported, though they were not treated until 14 to 48 days after the injuries. Six of the cats walked normally after a period of recovery and treatment, he said.

This is a field in which it can take time to confirm results, and some scientists yesterday said they were skeptical about being able to repeat Naftchi's results. But Naftchi called them "a breakthrough" that may ultimately help persons suffering from strokes and brain injuries, as well as spinal injury victims. He said some doctors have begun to try his approach.