Here's a statistic that'll probably shock the daylights out of you. It takes a net worth of $300,000 -- that's stocks, bonds, your house, your savings account, annuities, Social Security and whatever else you can turn into cash -- to retire comfortably, but not lavishly.

And five years out -- assuming an inflation rate of 8 percent -- you'll need assets of about $440,000 if you're going to stop working.

These figures, by the way, assume you will not invade your principal -- that you'll be able to live on a 10 percent return on your money ($30,00 now and $44,000 in the future).

These sobering thoughts on the economics of growing old comes from Bob Callender, vice chairman of Fairfield Communities of Little Rock, Ark., a leading developer of retirement and resort communities; (sales: $80 million).

Over the next 20 years, the fastest growing segment of the population will be the over-60 age group; it's grow 4 percent faster than the rest of the populace. We'll see the number of retirees -- those eligible for Social Security or equivalent-type benefits from local, state and federal government -- swell by 15 million over the next 19 years . . . from roughly 33 million in 1981 to 48 million in 2000.

An analysis by Fairfield -- based on findings after 16 years in business and the latest government data -- clearly shows that a lot of us are going to be in financial hot water when we retire.

We'll need, Callender tells me, approximately 35 percent of our after-tax disposable incomes as wage earners to maintain a comfortable standard of living upon retirement. And that assumes, he says, that eight out of every 10 retirees are willing to relocate to the less expensive South and Southwest.

The Fairfield study shows that only two of every 10 Americans financially are equipped to retire at their current standard lf living in such major metropolitan areas as New York, Chicago, Boston, Detroit, Philadelphia, Los Angeles and probably Houston in a few years.

And of the eight who will be forced to move from such cities -- unless, of course, they're willing to eat into their principal -- three will be required to adhere to a much more frugal existence.

A look at Social Security benefits -- from a program which itself may be in trouble -- clearly shows why the underground economy working for cash only is booming . . . and why, says Callender, it's attracting growing numbers of elderly to its ranks.

Under present SS benefits, a single person -- depending on the amount of time employed and his or her salary levels -- will receive anywhere from $153 to $685 monthly. For a retired married couple, the payout runs from $230 to $1,369.

On top of this, only one out of every two workers in private industry is covered by a pension and profit-sharing plan.

For a goodly number of Americans, as Fairfield sees it, the change from worker to retiree will be traumatic because of their sparse finances and the ongoing ravages of inflation. Among other things, he sees an increasing number of retirees having to spend their remaining days in mobile home parks, primarily in the South and Southwest. Used mobile homes in these parks generally will run around $12,000.