THE BANKING industry has been going out of its way to give substance to every left-wing caricature of bankers put in print since the days of William Jennings Bryan. Here is old moneybags jingling his way through the halls of Congress, not giving a hoot for the jobless or homeless, but simply intent upon preserving his God-given right to do business in the way he sees fit.

The banks' latest gambit--holding urgently needed money for unemployment benefits and emergency relief hostage to the repeal of withholding on interest and dividends--earned them a well- deserved rebuke from President Reagan. Noting that the banks' campaign has greatly distorted the withholding issue, the president suggested that "the banking industry would do a lot better to think about lowering interest rates."

We can think of other more substantial matters for the banks to pursue as well. The banks do not have a large stake in the withholding measure, but they have a very large stake in the expansion of International Monetary Fund quotas. This measure has been in trouble because it has been widely--but incorrectly--perceived as a bail-out for the banks. If the banks really want to do some useful lobbying, this should be their target.

What can be motivating this misdirected campaign? If you press the bankers on the subject, you'll get a lot of grossly inflated estimates of overhead costs. How can it be that the banks--which can provide 24-hour automated teller service, give you an instant reading on, or switch money between, any of your several accounts, and provide a daily statement of transactions arrayed in several dimensions--can't deduct 10 percent from your accumulated interest when they send the IRS the already-required notice of that interest? If it's so hard, why aren't the brokers complaining?

It is true that the banks have sown terror and confusion in the minds of many of their depositors. But that's their own fault, and they had best set about trying to reeducate their customers to the fact that withholding will impose no new tax or serious inconvenience on anyone.

About the only useful thing that has come out of this debate is the drawing of attention to the fact that the banks hardly pay any taxes at all. That piece of information will surely be useful to the people who make tax policy, but you may wonder whether the banks' stockholders feel that their interests have been well served by its prominent disclosure.

Nor can those stockholders be pleased that the banks have now managed to unite against themselves a coalition of right and left prominently led by President Reagan and Finance Committee Chairman Bob Dole. Is there no one in the industry with enough wit to see what the banks are doing to themselves?