CHANCES ARE that the statement you received last month from your bank or savings institution brought with it a special message of concern. The flier suggests that you, the customer, may wish to write your elected representative expressing your opposition to the new requirement that, starting next July, financial institutions withhold part of the taxes owed on interest and dividends.

Perhaps you overlooked this message because it arrived in an envelope stuffed with other communications trumpeting the many new services that your bank can now provide. Thanks to modern electronics, banks will now be pleased to shift your money back and forth among different types of accounts, calculate your accrued interest or account balance at a moment's notice and meet your banking needs day and night through automated tellers.

You might think that all this automation would make it easy for financial institutions to give Uncle Sam a helping hand in collecting the taxes he is owed. After all, employers have long been performing the far more complicated job of withholding taxes on wages paid, and you don't hear either companies or workers complaining. But to hear the banks tell it, this new requirement will impose a crushing burden on their operations and will discourage needed investment.

Your suspicions about these claims will be increased when you realize that, to help cover the cost of introducing withholding, banks will be allowed to retain withheld taxes for 30 days. This amounts to an interest-free loan of billions of taxpayer dollars. As for the impact on savings, most honest investors won't be affected at all.

No withholding is required on accounts earning less than $150 in interest or on those held by elderly people without substantial taxable income. People with substantial investment income are already supposed to be filing quarterly tax returns so that the new system will simply pay part of their taxes for them. And if you hadn't been paying the taxes you owed on interest and dividends until the end of the year, gradual tax withholding will still reduce your effective annual interest yield by less than five one-hundredths of one percent.

This is not a new tax. It is simply a way for the Treasury to collect taxes more promptly and more completely. It will impose no intolerable inconvenience on either you or your bank, and it will help the economy by reducing the annual budget deficit by several billion dollars.

All of this being so, you may wonder what the bank or savings institution is really saying in its message. Could it be suggesting that the only reason you entrust it with your savings is that you think you can hide that interest you earn from the tax collector? We trust that isn't so. And we hope that if you write your elected representatives it will be to say that you support this way of making sure that everyone pays his fair share of taxes.