WARNING BELL: From time to time, in the course of telling you about his product, an advertiser will include the words "tax deductible." This happens often in ads for investment publications, and is also found in appeals for charitable contributions.

The statement is only true with an important qualifier: " . . . if you itemize deductions." The cost of investment publications -- like tax advice books and the fee charged by a commercial tax preparer -- can only be claimed as a miscellaneous deduction on Schedule A.

The same thing is true, of course, for contributions to charitable organizations, for medical expenses, and for interest paid on a loan.

If you use the zero bracket amount (the old standard deduction) there is no place to take a deduction for any of these expenses. The amount is usually small; but don't count on recouping part of such payments through a tax dedution unles you expect to itemize on your next tax return.

Question: I have boxes full of old banks statements, cancelled checks, utility bills, charge account statements, etc. How long do I have to keep these papers?

Answer: There are several different categories of papers, with a different recommended retention period for each type.

Receipts and checks supporting your income tax return should be kept for three years after the due date of the return. This is because the IRS has three years in which to initiate an audit (unless there is evidence of fraud). But keep a copy of the return itself permanently.

Papers relating to the cost basis of your home -- purchase closing statement, bills and receipts for capital improvements, information about a casualty loss and insurance recovery, etc. -- should be kept at least three years after the due date of the tax return on which you report its sale or other disposition.

If tax liability is deferred because you have bought another home, then you must save the papers relating to each purchase and sale until after the last sale on which you account for all the previous transactions.

Documents relating to investment property -- real estate or securities, for instance -- should be saved until three years after the tax year during w,hich the property is sold.

Up to this point, I haven't saved you much storage space. Perhaps I can make up for that by telling you how I handle the other kinds of papers you mentioned.

I only keep bank statements, utility bills, and charge account statements for a month. When the following month's statement arrives, I compare closing and opening balances to be sure the correct amount has been carried forward -- then throw the old ones away.

Most cancelled checks have no particular importance either. Routine checks -- for cash or for food or similar purchases -- I discard immediately after reconciling the bank statement. Payments on charge accounts or utility bills are kept only until the statement comes in showing credit for the payment.

Only checks with tax implications -- like contributions to charity, medical bills, etc. -- and those relating to capital assets, as explained above, are retained.

A surprisingly large number of people like to hoard papers. Part of the problem may be that they don't really know what should be kept; so they keep everything rather than risk throwing away something they shouldn't. But cluttering up your house with stacks of unnecessary papers will only make it more difficult to find what you need when you need it.

Q:

Some time ago you wrote about saving tax money by using the standard deduction in alternate years, then shifting as many deductible expenses as possible into the year for itemizing. I have a lot of medical expenses, and my doctor now permits me to use a charge card. What date do I sue for the tax deduction?

A: If you pay for medical treatment with a bank credit card (or other charge card), the deduction counts in the year you charge, not the year you pay the bill.

It's the date of the actual use of the card, not the date of treatment, that governs. For example, if you go to your dentist for a series of treatments starting in November of this year, but you don't actually charge the bill until you finish in January, you don't prorate. It's a deduction for 1980, not 1979.

Incidentally, some religious and charitable organizations (Channel 26 WETA-TV, for instance) are now accepting contributions by bank credit card. The same rule holds; The deduction is claimed in the year the charge is made rather than the year of payment.

A column on family finances and taxes will appear in The Washington Post Business & Finance section on alternate Fridays. The author, E. M. Abramson, is a family financial counselot and tax adviser. Questions of general interest on tax matters, insurance, investments, estate planning and other aspects of family finances will be answered in the column. Advice cannot be given on an individual basis. Address all questions to E. M. Abramson, The Washington Post, Business & Finance News, 1150 15th St. NW, Washington D.C., 20071.