A soldier, an athlete, a Gov. Wallace, a motorcycle rider -- anyone -- is shot or gets into an accident that crushes or cuts his spinal cord.

The result has always been an irrevocable sentence to lifelong paraplegia: paralysis from the waist down, the fate of 150,000 Americans today.

The reason is simple and blunt: the main nerve cells of the spinal cord, once severed, cannot grow back together.

Or can they? Scores of the world's best neuroscientists have almost suddenly begun asking this question.

in the last five years there has been an almost complete reversal of opinion about this once hopeless area, several leading scientists agreed at a specially called symposium at the Wilson Center of the Smithsonian Institution last week.

"Let's not raise any false hopes -- we don't know how to solve the problem yet," said Dr. Donald Tower, head of the government's National Institute of Neurological and Communicative Disorders and Stroke, part of the National Institutes of Health.

"But the view that there is not hope of restoring the nerve pathways -- the view you would have heard from virtually every scientist not long ago -- is no longer held."

Two scientific leaders -- Dr. Lewis Thomas, president of Memorial Sloan-Kettering Cancer Center, and Dr. Arthur Upton, head of NIH's National Cancer Institute -- agreed that the time is ripe for what Thomas called a crash effort to collect information.

"I don't," Thomas emphasized, "mean a crash effort" like an Apollo or Manhattan project to produce a product -- the product here being the ultimate way to make the nerves grow -- but "a crash program to ask the questions" that could make that goal achievable.

"There is an awareness within the scientific community," he explained, "that an opportunity exists," that "it's time to go."

The "product," the method or knowledge that might make a paraplegic walk, could be "40 or 50 years off" or "a decade off" or "five years off," various scientists said.

But in the last five years, they reported, spending at NIH's neurological disease institute on the needed research has grown from $1 million to $7.6 million a year. The Veterans Administration has begun a $1 million-a-year program as a result of a strategy conference last year. Related scientifice papers in world literature increased from a handful in 1970 to nearly 500 last year.

What has happened in the scientists' laboratories to make so amazing a shift possible?

Beginning in the 1950s, said Tower, "A number of observations began to show that the mammalian nervous system does show evidence of attempts to regenerate itself. The machinery for regeneration seems to be there."

The machinery, in essence, is the nerve cell, a main cell body with long axons (or arms) often stretching, in the case of the central nervous system, the brain and spinal cord, very long distances. The spinal cord has millions of such cells, with axons reaching from the brain as far as the base of the spine, 2 or 2 1/2 feet away.

Tower said that in the last half-decade, in some cases the last few months:

"A lot of work" has helped scientists understand the molecular mechanisms, the processes that turn on and support the development of the central nervous system in infants.

Many studies, particularly those of Dr. Carl Cotman at the University of California at Irvine, have shown that in at least one area of the mammalian brain, severed nerve cells can sprout new connections.

Many people are looking at the "trophic factors," the elements or biochemical environments that make if possible for a severed nerve cell not only to sprout new connections but to make the right ones. It's no good for a nerve cell to sprout new fibers, Tower said, if they don't go to the right place to establish useful, not just random, motions.

Malcolm Wood and Melvin Cohen of Yale University reporting in the Oct. 19 issue of the magazine Science, have shown that if they sever the spinal cord neurons of nerve cells of lampreys -- eel-like sea creatures -- their axons regenerate and successfully form new synapses, or connections, with adjacent cells. And the lampreys again swim.

Wood and Cohen showed this by a promising new method -- a way of marking specific nerve fibers "so you know which ones you're looking at,' Tower said, "and that you're really looking at the important central nerve cells," not less important "local cells" that are easier to revive. The marking method is injection of a protein called HRP -- for horseradish peroxidase -- because it comes from the common horseradish.

Finally, Tower said, scientists have discovered new "nerve growth factors," proteins that combine with elements in the cells to help them grow. Rita Levi-Montalcini of the Laboratory of Cell Biology in Rome injected one such factor into the brains of young rats, and achieved not only growth of nerve cell axons but growth in a specific, desired direction.

Some researchers have attacked the problem more directly -- cutting the spinal cords or nerve cells of dogs, cats or rodents and trying to restore growth and function.

Last year Dr. Carl Kao, now of the Veterans Hospital and Georgetown University here, told of his work on dogs in Wisconsin, surgically destroying 40 dogs' spinal cords, then transplanting nerves to restore function -- even, apparently, walking -- in four dogs.

Critics say he did not prove regrowth of the important long axons in the nervous systems, and probably simulated only some useless walking-like reflexes in the animals' limbs.

Kao and his group are working with cats now, but he warned that there can be no application yet to human paraplegics.

"The science is not ready," he said at the Smithsonian. "we need more basic scientific information."

Dr. Albert Aguayo of McGill University, Montreal, who has also worked with small mammals -- rats and mice -- said, "You can get the axons to grow a few millimeters. But how do you get them to fill the gap" -- to grow enough to cross the synapse or connection between cells -- "so that's where we need basic research."

Dr. Richard Wyatt of St. Elizabeths Hospital and the National Institute of Mental Health told of his group's striking new work in grafting brain tissue from healthy to brain-damaged rats to alleviate movement disorders. It is possible, he said, that a grafting method might eventually help implant new nerve cells to correct human movement problems.

One thing scientists cannot say, these scientists emphasize, is where any new science will really take them.

The same facts that may or may not make nerve regeneration or nerve implants possible might combat diseases that attack nerve cells, like rabies and tetanus. Or the same information might combat the many nerve disorders that destroy normal movement, speech and intelligence.

What we can say," said NIH's Tower, "is that we've now got a lot of very bright people interested and working hard. And that's really the exciting thing. That's really the essential ingredient.

"We're now building up a critical mass that's inevitably going to pay some handsome dividends."