The stuff of science fiction and gruesome mythology is a hideous race of long-lived people, who spend the last half of their prolonged life spans in a state of helpless decrepitude, unable to find the peace of death.

Could this be where longevity research is heading?

Or is the goal to become a society of very, very old people who remain productive, functional, creative and wise for 120 years, 130 years, or even more?

"I think in every way a long-living society would be a better society than we have today," said Dr. Roy Walford, a pathologist at the University of California at Los Angeles whose popular books, "Maximum Life Span" and "The 120-Year Diet," advocate life extension through "undernutrition."

"Very old people get quite radical in their ideas, freed as they are of societal constraints," he said last week in Washington at the Gerontological Society of America's annual meeting. And with an increase in the number of the very old in society, especially if they are functionally younger than chronology would suggest, Walford added, "I think we can expect greater population diversity, multiple careers, intergenerational marriages, extended social networks."

Walford has established himself as one of the leading proponents of longevity. This vision, of course, is dependent on a plan for life extension that allows people to live a century and a half without aging at current rates.

Scientists have tried and rejected many techniques aimed at extending life: using drugs, vitamins or hormones; transplanting organs such as the thymus gland; removing organs like the spleen or pituitary.

But so far medicine's search for a fountain of youth has failed to break the conventional chronological barrier of about 115 years of age.

Walford's controversial approach to prolonging life involves a dramatic reduction of calories in the diet.

Based on animal studies and some suggestive evidence in humans, he said, caloric restriction may be expected to lengthen the maximum human life span to at least 140 years.

Walford pointed to natives of the Japanese island of Okinawa, who consume low-calorie diets -- about 60 percent of the national intake, with lots of fish and vegetables and very little rice, as human proof of his theory. He said Okinawans have a 60 percent lower death rate than other Japanese have. In addition, he said, they live to be 100 years old or more at a rate that is up to 40 times higher than anywhere else in Japan.

The added benefit of calorie restriction, said Walford, is that it would delay the onset of the degenerative diseases of aging, which now occurs between the ages of 60 and 80.

"It's probably biologically impossible to create a long-living society that is functionally decrepit," he said. "You can only create a long-living society if the people in it are functionally young."

But other experts at the conference were less sanguine about the vitality of a culture in which people live twice as long as most people do today.

Dr. Leonard Hayflick of the Center for Gerontological Studies at the University of Florida, Gainesville, conjured up the specter of the Struldbrugs from Jonathan Swift's book "Gulliver's Travels," who "never died, just got older and older and more disabled."

With most biological research aimed at eliminating disease, and therefore increasing average life expectancy without slowing the rate of aging, modern humanity may, like the Struldbrugs, be headed toward a "gerontological winter," Hayflick warned.

Hayflick worried, too, that if there were a medical anti-aging therapy, people would get lazy about sticking to such regimens. He pointed to the public's collective amnesia about the devastation of polio that helps account for the low immunization rate among preschoolers today.

"Would the same thing happen with an anti-aging regimen?" Hayflick asked. "I think it could result in neglect by the second generation, since no old people would be seen to remind the young people to adhere to it."

Speaking from a clinical perspective, Dr. Uriel Barzel, a geriatrician at the Montefiore Medical Center in New York, said that among the patients he sees, "for most people aging is an exercise in contraction." Slower reflexes, a greater tendency to fall, visual and hearing problems, and a decline in heart and lung capacity, he said, combine to make the lives of many of his oldest patients "miserable."

"Unless we are able to address these problems concurrent with the prolongation of life," said Barzel, "we are going to create a group of people who are more and more limited -- and less and less happy."

Walford remains an optimist, citing studies that suggest life prolongation and aging prevention might indeed go hand in hand. Among experimental rats and mice whose caloric intakes were restricted (down to levels as low as 40 to 50 percent of a normal diet), life spans were significantly longer -- up to half again as long as was normal for their species -- and, Walford said, many signs of aging were delayed.

Most of the speakers took it for granted that everyone would want to extend the life span as long as possible -- without thinking about some of social consequences.

"I'm not sure the banishment of death to its furthest point is even a good goal," said Dr. Nancy Dubler of the Division of Legal and Ethical Issues in Health Care at the Montefiore Medical Center. She said artists, poets and composers have long found "that the concept of death and its imminence heightened our awareness of life." Are people willing to give up the intensity of that awareness?

And death may serve more than an esthetic function, she said; it may have a social role as well. In an unequal society such as ours, "the ability of poor people to regroup their assets on the death of an elder means that the younger ones have a new chance." So while as long a life as possible might be an individual goal, she said, "I'm not sure it's a societal goal."

Dr. Christine Cassel of the University of Chicago School of Medicine likened the debate on the ethics of longevity research to a similar debate that took place 15 years ago on the ethics of recombinant DNA research. "But there's one big difference," she said. "Most people here today are concerned not with the direct effects of the research, but with our inability as a social body to deal with its success."

And unlike the imagined hazards of recombinant DNA research, she said, the problems envisioned as a result of extending the human life span "are open to our solution."

Cassel said her 96-year-old grandmother, though still "sharp as a tack," was ready for death because she had completed what she had set out to do with her life. If individuals are to live 40 or 50 years longer than even her own long-lived grandmother did, she said, they must be given something important to do with all that extra time.

"A long life is desirable only if life is good," she said. "That doesn't mean everyone has to be vibrantly healthy at 110, but it does mean your role in society has to be a real one. The added time achieved shouldn't just be a matter of waiting."

An unidentified scientist in the audience, criticizing the panelists for not being more imaginative in their vision of the future, had his own view of the benefit of extending the human life span: "A long-lived species could own the universe," he said. "The distances between the stars, if you can live for 200 years, become a very small part of a lifetime." Robin Henig is a Washington-based free-lance writer.