If my mail is any guide, bank errors are driving customers crazy. The more complicated banking gets, the more mistakes get made -- and it can take days to straighten things out. But there are a few precautions you can take:

*Cash. How many times have you cashed a check in a hurry and walked away from the teller's window without bothering to count the money? That's a sure formula for losing money someday.

If a teller accidentally shortchanges you, your only hope of collecting the missing money may be to discover the error right there at the counter. One woman tells me that she cashed a check, took the money to another spot in the bank to count it, and came up $20 short. But when she went back to the teller, it was too late. Tellers aren't allowed to pay out extra money on your say-so.

What to do in a case like this? Explain what happened to both the teller and the manager, and give them your name, address and phone number. The bank will reimburse you if, at the end of the day, the money in the teller's drawer shows an overage by the amount you claim you were shortchanged.

*Multiple Checks. Tellers sometimes count better than they add or subtract. Say, for example, that you give a teller three checks in varying, odd amounts, plus a deposit slip showing that only part of the money goes into your account. You want the rest of it in cash. Amid all these transactions, the teller might give you the wrong amount of cash.

The best way to catch this kind of mistake is to work out in advance how much cash you should get.

*Automated Tellers. Stories about ATM errors are piling up. Some machines mislay your money. Some forget to credit a deposit to your account. Some pay out the wrong amount of cash. There are three ways of keeping an ATM in line:

First, always keep a copy of your deposit slip and check it against your monthly statement. "It always amazes me to see the trashbaskets near ATMs overflowing with deposit slips," says the American Bankers Association's Dan Buzer. "If a bank credits one of those deposits incorrectly, how would you know?"

(The commonest errors are for a clerk to enter a digit wrong when a deposit or withdrawal is posted to your account, or to add or subtract a zero. What if the error runs in your favor -- say a credit of $1,000 when you deposited only $100? Don't spend the money! If you don't report the mistake, the bank will find it when the accounts are balanced. In the world of finance, there is no such thing as finders-keepers.)

If an ATM loses one of your checks, the bank can usually trace it even if you don't have the deposit slip -- especially if you can remember the day you deposited it.

If the bank bounces any checks that you wrote against the check it lost, you should not have to pay a bounced-check fee. Write the manager a frosty letter demanding that the bank find the missing check (enclose a copy of your deposit slip), write letters to your creditors explaining that the checks were bounced in error and rescind the charges. He or she should do exactly that.

Second, never put cash into an ATM, because if it's mislaid it's harder to recover. Yes, your deposit slip "says" how much money you put in. But there is no legal proof that you actually deposited as much cash as the slip records.

If an ATM does swallow your cash, tell the bank about it, leaving your name, address, phone number and the size of your loss. If, when the ATM's accounts are balanced, its cash is over by the amount you reported, you should get your money back.

Third, try to use the ATMs in bank lobbies or that come equipped with telephones that go directly to the bank. If a machine shortchanges you -- say, giving you $90 when you tried to withdraw $100 -- you can then report it instantly. The sooner you make such a claim, the more credibility it has. Even so, you will probably have to wait until the accounts are balanced before the bank will produce the money due.

*Forgeries. If someone forges your signature on a check, and the bank cashes it, the fault is always the bank's. It doesn't matter that you may have been careless with your checks. You are entitled to be 100 percent reimbursed.