A retired American today is probably the freest human being ever to walk the earth.

Assuming that basic needs are met by a pension, Social Security, Medicare and investment income, the retiree lives in a perpetual paradise of leisure and recreation. If the retiree stays healthy, this special status can be enjoyed for 15 to 20 years. There is time to fish all day or golf every afternoon.But retirement in the United States is also frightfully expensive - both for the nation and for those who pay the bills.

The high cost comes not only in payments to the retired, but from production lost when part of the labor force sits on its hands. This forgone production creates a serious problem that can only get bigger.

Considering only healthy people aged 65 and over, the United States loses about 17.5 million older workers through complete retirement - about 14 percent of the total civilian labor force.

So far, however, this loss has been more than made up by the entry of married women into the labor force. But this bonanza will not last long.

Indeed, as the graying of America continues, fewer and fewer workers will pay for more and more senior citizens. In 1970, there were four workers for every nonworking retiree. By 1995 there will be only three to support each retiree.

These retired Americans have been told they have worked hard and now deserve their leisure. The average person retiring at age 63 still has 18 years to live (16 for men). This is equivalent to 42 percent of the average person's working life.

This is not only a considerable amount of time to spend fishing and golfing, but it is also a long time to spend dependent on others.

And what about the direct costs to support what could be called a privileged group of idle senior citizens?

With 87 percent of men and 93 percent of women 65 and over not working, the economy is paying a high price for retiree heaven.

Federal benefits for the elderly in 1985 amounted to nearly $264 billion, about 28 percent of all government expenditures - including defense. And, as the population grows older, the burden on the labor force will become even more onerous.

What should we do? Reducing retirement benefits is probably harder to achieve than getting people to remain in the workforce. Once support of retirees becomes impersonal - a charge on the general public rather than on grown children - there is no moral constraint on their economic demands.

Further, the elderly are so numerous, so articulate and experienced, and so possessed of free time (since they are not working) they can and do lobby powerfully for their own interests.

One path that could be taken is the one chosen by Japan. The Japanese assume that individuals will continue to work as long as they are able. Japan thus escapes the financial burden of a vast army of able but unproductive citizens.

As a matter of tradition, Japanese workers usually retire before 60 years of age, but they do not quit working. They lose seniority, their normal salary, their usual authority, but not the chance to work. Often, in fact, they are rehired by the same company, but in a less demanding position.

In retiring so early, Japanese workers have a better chance to adapt to their new circumstances and, thus, not drop entirely out of the work force.

No surprise, then, that Japan has a higher proportion of men aged 65 and over in the labor force than any other industrial country.

For example, in 1980, 65 percent of Japanese men between the ages of 65 and 69 worked, compared with just less than 30 percent in the United States. Even among Japanese 80 and over, 18 percent are employed, compared with almost none in the United States.

I am not advocating any specific scheme, although I oppose mandatory retirement rules. But, by 1990, there will be approximately 32 million older adults in the United States whose contribution to economic production will be zero. That is a luxury this nation may not be able to afford.

(Kingsley Davis teaches sociology at the University of Southern California.)