The flu season is upon us. For millions of older Americans, this may mean more than just a few days at home with the sniffles. The flu season could produce increased medical costs, hospitalization - and even death from complicating illnesses.

Elderly people have good reason to fear the flu. Because of age and chronic ailments, they are more suceptible than others to severe illness and complications such as pneumonia, encephalitis and kidney failure. From 1972 to 1978 (the latest data available), more than 97,000 elderly Americans died from influenza.

While it would be impossible to measure the human misery resulting from flu, the financial cost of treatment can be calculated - and it is astronomically high. From 1972 to 1978, more than $1.07 billion was spent by older Americans for treatment of influenza. Most of the cost fell on the elderly themselves, and on Medicare. The great tragedy is that the deaths and the high cost of treating flu victims among senior citizens could have been avoided.

Since the early 1960's, a simple, safe and effective preventive vaccine has been available. Medical experts agree that vaccination is the preferred method of preventing influenza. With such an obvious way to avoid the flu, why is it that no more than 10 percent to 20 percent of our older citizens have taken advantage of vaccinations in the last decade?

Health professionals, spokesmen for organizations representing the elderly and Congressional investigations generally focus on two of the major considerations: money and the disastrous ''swine flu'' vaccination program of 1976. The major failure of the swine flu program - isolated instances of adverse reaction and 32 reported deaths out of 45 million immunizations - were an aberration when compared to the overall success of influenza inoculation programs. But they did leave many older Americans with vague discomfort about the safety and effectiveness of flu vaccines in general. Government agencies have been slow to take aggressive action in this field since being so badly burned in 1976.

Overcoming the second impediment, money, is more complicated. An overwhelming majority of the elderly cannot afford to get flu shots privately, and the Administration is in no mood to help provide the funds.

Ironically, under current law, the Medicare program provides reimbursement for medical costs associated with treating flu after it has been contracted, but it does not cover the cost of taking measures to prevent the illness, like vaccination. Curing illness is always more expensive, and causes far greater suffering, than the preventive care that could have avoided a malady. This Medicare policy makes neither good medical sense nor good economic sense.

At a hearing last year in New York City about flu shots, representatives of national senior citizens' organizations, as well as elderly local residents, agonized over the choices older Americans must make during cold winter months - choices between paying heating bills and buying food or paying for flu shots. Not surprisingly, witness after witness testified that flu immunizations were at the bottom of their priority list.

Clearly, Medicare policy deters older Americans from taking preventive measures they know are in their best interest. The Medicare law must be changed to cover preventive flu shots.

At the hearing, the Congressional Office of Technology Assessment presented the results of a dramatic study highlighting the costeffectiveness of flu vaccine, particularly for the elderly. The study showed that for high-risk elderly people, preventive inoculations produced an extra month of healthy life at a cost of only $2 and an extra year of healthy life at a net savings in medical expenditures.

Congress took strong action in 1980 in a related area following a similar study of the cost-effectiveness of pneumonia vaccine by amending the Medicare law to cover the cost of preventive inoculations. Despite the Administration's attempts to repeal that provision, Medicare continues to pay for prevention of pneumonia among the elderly. Now that the nation knows the Office of Technology Assessment's findings on influenza vaccination, the time has come for Congress to take similar preventive action on flu shots. The evidence is clear: These shots prevent illness and ultimately save Federal dollars. Budget-slashers may ask: Can we afford to add flu immunizations to the Medicare package? But at a time when hospital costs are rising at an annual rate of 18 percent, the more appropriate question is: Can we really afford not to?