ST. LOUIS — Arthur Berrier and Irene McAnally are still exceptions in our society.

They've both made it past their 100th birthdays, living healthy, productive lives. They've seen their children grow to old age and their grandchildren mature and become parents themselves.

But the rare status enjoyed by centenarians such as these is likely to change.

Scientists are predicting that new technologies could extend the average person's life span decades or longer.

Much longer.

It may be possible, according to one theory, to increase longevity virtually indefinitely, making Biblical life spans of hundreds of years, even 1,000 years, a reality.

Just adding several decades — among the more modest predictions to be offered — would have enormous consequences for society, experts say. If scientists could turn their anti-aging hopes into reality, life expectancy might climb from 76 years currently to 101 in 2050. The median age in the United States would rise from 35 to 48. About a fourth of the population would be older than 100.

In a session recently at the annual meeting of the American Association for the Advancement of Science, researchers clashed over how long humans might one day live. But they all agreed that the prospects were good for adding decades.

"People alive today may be able to live indefinitely," was the startling claim by Aubrey de Grey, a biomedical gerontologist at the University of Cambridge.

Of course, if people live much, much longer, retirement accounts would be emptied and health-care resources would be strained.

"If we live another 30 years, that's a substantial amount of money, and it has to come from somewhere," said Shripad Tuljapurkar, a professor of population studies at Stanford University who has been making such projections.

Aging occurs as the body becomes less able to cope with the byproducts of metabolism and other chemical processes that make life possible.

Exercise becomes harder; thinking gets slower. Eyesight dims. Bones grow frail.

Halting the aging process completely is far beyond the current understanding of science, de Grey said. Instead, researchers should act like engineers, repairing damage to the body's cells and tissues before it progresses to disease.

The techniques for doing that are within reach, according to de Grey.

"The engineering process is more realistic," de Grey said. "Repairing, reversing or in some cases making harmless the damage caused by metabolism."

Given enough financial resources, scientists have a 90 percent chance of doubling the life span of laboratory mice in 10 years, de Grey said. Given 15 more years, they have a 50 percent chance of doubling the remaining life span of a 55-year-old.

De Grey's claims have raised a storm of criticism in the scientific community. A group of prominent scientists went so far as to call his ideas more science fantasy than fact.

One of those researchers, Steven Austad of the University of Texas Health Science Center, spoke at the meeting immediately after de Grey. Austad dismissed de Grey's ideas as mere "thought experiments."

Austad agreed, however, that progress in delaying aging would come in the next couple of decades.

People will live to be 150, he predicted.

"I think that person is alive right now," he said.

But slowing the aging process will not be as easy as de Grey suggested, Austad said, and it could have side effects.

For example, scientists have been studying the Ames dwarf mouse, which differs genetically from average mice. The Ames mouse lives 50 percent longer and retains its ability to learn well into old age. But the mouse is very slow on its feet.

"If you put an Ames mouse out in the field, it would be dead before tomorrow," Austad said.