The news about immortality, so scientists tell us, is not so good, but that's no cause for giving up when we start getting old. For one thing, the news about being old is getting better.

The leading edge of gerontological thought, as the science of aging is known, is leaning heavily to the theory that the human machine has a built-in limit on how long it will function. At some point, scientists have found, cells simply stop regenerating. Scientists differ on how much -- or even whether -- this built-in biological clock's relentless ticking can be slowed down.

At the same time one group is saying forget it, there is no fountain of youth, there are plenty of others who say, yes, well maybe so, but there's no reason to fall apart at, say, 60, when 85 or 90 good years are often attainable.

So it isn't so much how long can I stay alive, but rather how can I stay mentally and physically fit as long as my body clock still has time on it.

Dr. James Fries, author, lecturer and head of the Stanford University Arthritis Clinic, is a firm believer in the theory that, as he wrote in a recent special article in the New England Journal of Medicine, "The body, to an increasing degree, is now felt to rust out rather than wear out."

He has, for years, told his arthritis patients to exercise: "Use it or lose it." In other words, the body need not "rust out."

"If loss of reserve function represents aging in some sense," he writes, "then exercising an organ presents a strategy for modifying the aging process." "

Chronic diseases, notes Fries, now account "for more than 80 percent of all deaths and for an even higher fraction of cases of total disability." As these are either prevented, or vastly ameliorated, by a combination of medical techniques and patient self-responsibility, "The end of the period of adult vigor will come later than it used to."

Fries' approach is thoughtful, philosophical and profound. It embraces the relationship between medicine and people, and explores -- in fact predicts -- the full acceptance of the concept of death as no more than an inevitable, but unfeared end to a long and fully lived life.

Joe Graedon views the matter with ultimate pragmatism. The author of "The People's Pharmacy," and his current update "The People's Pharmacy-2" (Avon, $5.95), feels that a combination of doctors, drug companies and assembly-line pharmacies are robbing senior citizens of their chance to live out their years with the quality of their lives as little impaired as possible.

Philosophically, he would not disagree with Fries, but where the Stanford physician is concerned with universal concepts, Graedon's message is to the man he calls "good old George," and his specialty is in the use of medicines, rather than in the practice of medicine.

As people age, says Graedon, they "tend to be much more susceptible to side effects (of medicines) because they can't metabolize or eliminate the drugs as easily as they did when they were younger."

For one thing, he says, "Kidney function tends to be reduced as you get older, so there is a greater likelihood of drugs accumulating in the body. The other thing is the dose. Older people tend to be thinner. There is relatively more fat and less muscle. So what is an appropriate dose for a 40- or 50-year-old can change dramatically for the 60- or 70-year-old." Yesterday's perfect dose may be tomorrow's fatal "O.D."

Graedon's thesis, based on today's essentially sedentary older majority rather than on those who better meet Fries' old-man-of-the-future-model, finds "good old George" going to more and more doctors for "more and more degenerative problems." Or they have been under treatment for one of the common chronic illnesses for 20 years and no one has bothered to change the dosage. Maybe the drug manufacturer has actually changed the recommended dosage, but no one remembers George is taking that drug.

"It can," says Graedon, "be a very frustrating and demeaning experience to go to the doctor when you're in your 70s and 80s, to be kind of put on the conveyer belt, rushed through. The doctor is not really listening to your problems, because a lot of times it may just be a case of wanting a sympathetic ear.

"To today's specialists, you become a crock, a geezer, a gomer." (A "gomer," it has been suggested, is medical-ese for "get out of my emergency room.")

Graedon believes in a revolution of senior citizens.

"You have a right," he tells them, "to know what side effects any drug you get may have."

You have a right to say no if the side effect, say impotence (in some blood-pressure medicines), is deemed by you to be worse than the control of the condition at which it is aimed. You have a right to be told what vitamins don't go with which drugs. Among examples from Graedon's book:

El Dopa, a drug used to control Parkinson's Disease, may be inactivated by a vitamin pill containing Vitamin B-6. An iron supplement is useless when taken with tea, hot or iced -- unless there is milk in the tea. Milk, a wonderful source of calcium, can be made perfectly digestable to older people, and others with a lactose intolerance, by the simple addition of a substitute lactase enzyme available from most pharmacies without a prescription.

Almost most of all, Joe Graedon mourns the disappearance of the old mom-and-pop pharmacy where good old George's pharmacist made up the formulation unique to George's problem, where he knew if another doctor prescribed something that wouldn't go with the medicine prescribed by the first doctor, where he'd get the message to George that the company had changed the dosage.

"You can," says Graedon, "just kiss the old-time pharmacist goodbye." Finding out is "now the responsiblity of the consumer."

"And I think that's a shame."