BY NOW YOU are surely aware that the opportunity to amass a million dollars lies no farther than the door to your friendly neighborhood savings and loan or other investment outlet. This chance of a lifetime is brought to you courtesy of the new Individual Retirement Account (IRA) provisions added to the tax law last summer, which allow every wage earner to salt away $2,000 each year without having to pay income tax on it until retirement.

Banks, savings and loans, mutual funds and life insurance companies are now vying for the happy business of putting you on easy street in your golden years. The other day this paper carried a typical advertisement--this one by New York Life Insurance and Annuity Corporation--promising that, if you invest in their IRA flexible annuity, "your $2,000 can grow to more than $1,500,000."

Some important qualifications are noted in the ad. To get this return you have to continue to invest $2,000 for each of the next 40 years, and when you withdraw either your principal or your earned interest, you'll have to pay ordinary income tax on your withdrawal. New York Life is also assuming in its calculation--but not guaranteeing--that the going rate of interest on deposits of this type stays, on average, at its current 12 percent level. Still, that seems like a pretty good deal. Where's the catch?

>The catch, of course, lies in that interest-rate projection. Assuming that interest rates average 12 percent over the next 40 years is tantamount to assuming that inflation will average about 10 percent over the same period. If inflation is lower, so will be your interest. This should make you wonder what your "more than $1,500,000" will be worth in current terms when you fall into it in the year 2022. In case you don't have your calculator handy, we'll tell you the answer.

Investing $2,000 for each of 40 years at 12 percent interest will leave you with over a million and a half dollars--$1,534,183 to be precise. But, after 40 years of 10 percent inflation, that nest egg will be worth only $33,898 in terms of current purchasing power. After paying taxes, that will still leave enough for, say, a down payment on a modest retirement home, but it won't keep you living like a Rockefeller. In fact, it's not even enough to retire on.

It's interesting to note, however, that if inflation suddenly fell to zero and stayed there and interest rates then settled at a corresponding 2 percent, your accumulated savings over 40 years would be $120,804--and that would be worth just as much then as it is today. You'd be much better off partly because your $2,000 deposits in later years would be worth more than if double-digit inflation had been running in the interim, but also because your interest accumulations wouldn't be eroded by inflation.

There is a moral in all this--not just for the people to whom these advertisements are directed, but also for the companies doing the advertising. It is this: if inflation stays as high as the advertisers are assuming in their be-a-millionaire calculations, fixed-annuity investments are going to be so unattractive in future years that the people pushing them are likely to find themselves in some other line of business--if they are in business at all.