If you're among the millions of Americans whose credit histories aren't quite perfect, answer these questions:

* Have you been trying to improve your credit standing by scrupulously paying your mortgage and credit card bills on time every month?

* Would you be upset to learn that your solid, on-time payment performance isn't being documented anywhere, and therefore won't help you get a lower interest rate the next time you apply for a home mortgage or an equity loan?

Get ready to be upset. Federal officials and private-sector credit agencies say the practice of not reporting mortgage and credit card payment performance is abusive and widespread. Federal financial regulators recently issued an advisory to the nation's banks urging them to take defensive steps to guard against the potentially harmful effects of the practice.

Here's what's involved: You might assume that all your major credit transactions--how much you borrowed on your mortgage, the limit on your credit card--show up in your credit files. But that's not the case, especially if you're a homeowner with some minor dents in your payment history.

That's because some mortgage lenders and credit card companies hide you from potential competitors. They no longer report your payment histories to the three national credit reporting bureaus--Equifax, Experian and Trans Union. According to federal officials familiar with the practice, that's because they want to keep other lenders from knowing how solid and profitable your account is. Aggressive lenders routinely surf through credit files electronically to identify and harvest potential prospects for home refinancings, home equity credit lines and credit card offers.

Among the most attractive prospects are people who are paying higher-than-market interest rates on their mortgages because of prior credit problems, but who make their payments on time every month. Many of them expect their on-time payments to help reestablish their credit records and enable them to qualify for lower rates in the future.

That's not necessarily true. Nonreporting of payment performances by some mortgage lenders means their customers "aren't getting a fair shake," said Deputy Comptroller of the Currency David Gibbon. They're caught in a self-fulfilling prophecy: They started out as borrowers with inferior credit, but because their excellent recent performance is not being reported to the credit bureaus, their files show no improvements.

Gibbons believes the practice of selective nonreporting could have fair-lending implications as well. If statistical studies showing that minority groups are more likely to carry subpar credit scores than other groups are correct, he said, minorities--especially African Americans and Hispanics--could be hurt by nonreporting more than other consumers.

Financial regulators decline to identify companies that engage in nonreporting, but they say some are among the largest lenders in the United States. For its part, an organization representing nearly 400 consumer lenders, the American Financial Services Association, announced last week that its members have agreed not to withhold borrower information from credit bureaus. Among the companies covered by the pledge are giants including Norwest Financial, GE Capital and Household International. Last year, Household--a major home equity lender--confirmed that it engaged in selective nonreporting as a defensive measure against competitors.

Last week's advisory letter to banks, issued by the five major financial regulatory agencies, focused on the flip side of the nonreporting problem--the implications for the "safety and soundness" of financial institutions that lend to consumers whose credit files are incomplete. Banks evaluating loan requests from borrowers who have frequently been late--but haven't been documented as such because their lender doesn't report to credit bureaus--"could inadvertently expose themselves to increased . . . risk." The advisory urged banks to devise ways to protect themselves against lending blindly to applicants whose credit records are "incomplete."

Aside from the banks' problems, what about consumers being victimized by this failure to report payments? What can you do to guard against it?

One suggestion is to periodically obtain copies of your credit report from the three bureaus and look for missing data. Has your mortgage lender regularly reported your payments? Does your credit card company report all the information it should, such as your credit limit? If you discover information missing in one or more of your reports, demand that your lender tell you why.

There's a second action you might consider. Did your lender promise or imply that by taking out your current loan and repaying it on time, you could improve your credit score in the future? And do you now find that the same lender isn't even sharing information about your on-time performance with the credit bureaus that maintain your files and compute your credit score? Sounds like that could be a false and deceptive trade practice that your state attorney general, or even the Federal Trade Commission, might like to learn about.