Time's a-wastin'. You only have until April 15 to open an IRA or to make payments to an existing IRA on 1984 earnings. The rules have been changed -- last year you could delay your deposit to Aug. 15 if you had asked for a four-month extension for filing your income tax return.

An Individual Retirement Account is probably the best tax shelter the average person can find. But according to the Investment Company Institute, by early this year only about 20 million Americans had IRAs, out of an estimated 83 million who are eligible.

If you're eligible for an IRA but don't have the cash in hand, you might consider borrowing to finance your 1984 deposit. Borrowing can actually save you money in the long run, by providing a tax deduction that is greater than the interest cost.

Here's an example. Wanda Worker is in the 26 percent tax bracket for 1984. She would like to put at least $1,000 into her IRA for 1984, but she doesn't have the cash. What she does have is a $700 refund coming on her federal income tax return, and another $150 on her state return.

So she borrows $1,000 from her local credit union, which she promptly deposits in an IRA there. She changes her tax returns to reflect the IRA deduction and sends them in. Because of the $1,000 IRA deduction, Wanda now can expect $960 from Uncle Sam and a little over $200 from the state.

Three months later she has both refunds in hand and repays her credit union loan. At 15 percent, the interest cost of the loan comes to $37.50 (which she can claim as a Schedule A deduction, if she itemizes, on her 1985 return).

In return for the $37.50 cost of the loan, Wanda has reduced her federal income tax liability by $260 and her state tax by $57.50 (Virginia rate). So she now has $1,000 in her 1984 IRA, and has saved $200 in tax money doing it.

Of course, borrowing to finance your IRA is not smart if you have no firm prospect of being able to repay the loan. I know very well there are people out there who are living so close to the line that they simply can't squeeze out a buck for retirement money.

But if you're facing a temporary shortage and can see a good chance to repay the money you borrow, either from a tax refund or perhaps in regular monthly payments, then think about a short-term loan to fund your IRA and let the tax collectors help you repay the money.

Q: I was interested in your answer in the Dec. 31 column to a question about reporting gains and losses in an IRA. You said, "Your best bet in an IRA is usually an investment expected to generate current income rather than long-term growth -- income that would otherwise be taxable." Do you imply that there is some way to get gains that wouldn't be taxed -- even when they're withdrawn from the IRA? And what kind of investments, other than bank certificates of deposit (CDs), would fall into this category?

A: Sure, there's a way to get gains that won't be taxed -- but not within an IRA. If you invest in an asset -- say, 100 shares of stock -- outside your IRA and hold it for more than six months, then only 40 percent of your gain on the sale will be taxed. You get to keep the other 60 percent of the gain without tax liability.

But if you have a self-directed IRA and buy that same stock, any gain on a later sale loses its indentity and is simply combined with other earnings on assets in your IRA. When you retire and start to withdraw funds from the IRA, all withdrawals are taxable in full in the year received -- you lose the capital gain tax break normally available.

That's why I said that usually it is advantageous to hold growth assets -- assets expected to generate capital gains -- outside the IRA, and concentrate your IRA money in those assets normally expected to produce current income to be reinvested.

To answer your further question about what kinds of investment other than bank CDs would fall in this category, think about corporate bonds, income-producing stocks such as public utilities, income-oriented oil and real estate partnerships, money market funds and mutual funds investing for income rather than growth. And I assume that when you say "bank CDs" you include CDs from other financial institutions such as S&Ls and credit unions.