No law seems more misunderstood than the one that grants credit rights to women. Angry letters continually turn up in my mail from women who think a lender did them wrong. In fact, most of my correspondents, including businesswomen, don't really know what credit rights are and how they are applied. Here's who is complaining:

Married women who think they're being discriminated against but probably aren't. (More about that below.)

Single women who think they've established their credit histories but haven't kept on top of it. If they marry and change their name, they must get their credit transferred, too. Every time you apply for credit you should use the same name to keep your history together.

Widows and divorced women who have lost their marital credit history. They may have only themselves to blame because they didn't establish their own credit when they had the chance.

By now, I think every married woman knows that she should get credit in her own name. What they don't understand is what that phrase means.

You have your own credit if your jointly held accounts are reported in your name -- Joan Johnson -- as well as your husband's name. That's all.

The account can be based on his income, your income or both incomes.

It does not mean that you must qualify for credit on the basis of your own income alone. Working wives who try that route are probably going to be turned down.

Why? Take the case of a Pennsylvania reader who runs a small business. She applied for some charge accounts, putting down only her own earnings, and was turned down.

Her rejection slips said that she wasn't making enough money to qualify for credit. This astounded and angered her.

When she looked at her credit report, she found the reason. She and her husband have joint debts, including a mortgage. If he doesn't pay, she is responsible. The lender set the couple's joint obligations against her single income and quite properly concluded that she couldn't support an even larger load of debt.

To her, that sounded unfair. But it's not. "A lot of women have a major disconnect with reality," said Delia Fernandez, public affairs director for TRW Information Services, a leading credit-reporting service. "She's legally responsible for that joint debt. Even cosigning a loan will show up on your credit report, because it's an obligation."

In community property states, married women are generally liable for their husband's debts even if they don't cosign them.

The good news is that the reader in Pennsylvania -- and everyone like her -- has her own credit, even though she doesn't realize it.

"Your own credit" simply means that, when a lender asks about you, a report shows up in your name -- Joan, not Mrs. John. The "Mrs. John" record belongs to your husband.

All accounts opened for married persons after June 1, l977, are reported in both names.

For accounts opened earlier, wives must ask the store or bank to report the data in their names as well as their husband's.

If a wife wants to show that she can repay by herself, here's how: Buy a car, apply for the loan yourself and have your husband cosign. It will show on your credit history as your own debt. Requiring a cosigner is not discriminatory if the woman has no income, or insufficient income to meet all her personal and joint obligations.

Warning: Some women allow themselves to be designated as "authorized users" on their husband's accounts without taking on personal liability for the debts. Such an account will be reported in your name, according to Federal Trade Commission attorney Sandra Wilmore.

Credit grantors usually give it the same weight as joint accounts in judging your reliability. But, adds Delores Smith of the Federal Reserve, a creditor could yank the card if the husband dies.

By contrast, a widow who is jointly liable for the debt can't have her credit revoked unless she shows inability to repay.

If you separate from your husband, be sure that all joint debts continue to be repaid. Note that some "authorized users" may also be jointly liable, either for the whole account or for the specific charges she signs herself. Check your credit agreement. Otherwise, it will soil your record as well as his.