THE AVERAGE American will soon have several more years of life to look forward to. Moreover, thanks to medical advances and healthier habits, most people won't have to spend those added years nodding in nursing homes. Two medical professors brought these tidings to a conference of scientists meeting here last week.

That is good news for people at the stage in life when old age suddenly no longer seems like something that only happens to somebody else. But will people retiring over the next several decades have enough money to support at least a modestly enjoyable old age?

For the next couple of decades, there is little cause for alarm. The generations entering retirement--including the sparse ranks of those born in the Depression era--will have behind them the huge cohort born during the post World War II "baby-boom." Unless the economy stays very sour, Social Security coffers should be overflowing. After that, however, watch out! As the baby-boom people start to retire, the actuaries tell us, the ratio of workers to retirees will drop to only two to one.

The elderly are already a potent political force in America--witness the very light treatment that the administration gave to programs for the aged in last year's budget cuts. Government support for the old already accounts for about 30 percent of the federal budget. If you want to take a dire view of the future, you can imagine that, by the second quarter of the next century, the elderly--whose numbers will have doubled--will be able to vote themselves still more generous public benefits to be financed through the efforts of a dwindling number of workers. Or you might envision a situation in which the working population rises up against the increasing claims of their elders and abruptly cuts back their supports.

Presumably something will intervene between now and then to forestall so sharp a conflict. The choices, however, are limited. Nothing can be done about the large bulge in the population that will be retiring in the next century. But one important factor could be reversed--the trend toward ever-earlier retirement. Many factors--age discrimination, pension policies and high unemployment--have promoted early retirement. Personal preference, however, has played a large part. While the elderly support changes that would allow older workers to keep their jobs if they want to, the idea of postponing pension benefits has been strongly resisted.

When you're talking about something as important as planning for old age, it is important that any change be introduced gradually. For that reason, it's not too early to start considering whether future generations of people in their 60s--with their expectation of longer, healthier lives--might not find it quite acceptable to work a few years longer to ensure themselves of a financially secure retirement.