While science strives to achieve the glamorous goal of increasing our life span, most researchers studying aging are concerned with a more practical problem.

Do we really want to live longer?

According to a group of researchers who study the consequences of being old, living longer might be of little value unless the extra years are healthy and active.

Despite recent gains in life expectancy caused by lower death rates from heart problems and other major fatal diseases, many of the nation's elderly are troubled by generally nonfatal ailments and disabilities during their final years, gerontologists say. These conditions include Alzheimer's disease, blindness, deafness, arthritis, osteoporosis, diabetes, hypertension, incontinence and physical frailty.

"These are the things that, for the most part, don't kill us. But they make life difficult in old age," says medical demographer S. Jay Olshansky of the Argonne National Laboratory in Illinois. "If you ask people what stops them from enjoying life in old age, many are going to say those diseases."

Olshansky is co-author of a recent study published in Science magazine that asks if efforts to expand life should continue without equal emphasis on making the last years quality years.

Scientists have made astounding gains in the past decade in understanding the process of aging, giving rise to hopes that they might someday postpone its effects through genetic engineering.

Another arm of longevity research concerns eradicating the major killers--such as cancer and heart disease--to reduce death rates and prolong life. Advances in heart disease treatment have already led to gains in life expectancy over the past two decades, experts say.

But, Olshansky says: "What I worry about is if we are successful in identifying what causes us to age, if we find an anti-aging drug or find a way to manipulate genes, then we are faced with the social problem of whether we really want to do that.

"If we can extend life expectancy by 10 years or 20 years, we need to be assured that the additional years of life are healthy years. If we are adding 30 years of crippling disease, then I don't think we should do it."

The question is not merely philosophical. Policy-makers are increasingly interested in understanding the future impact on health care and Social Security as the baby-boom population turns the corner on middle age.