A new national study on credit scoring describes widespread problems that could affect the mortgage rates paid by millions of home buyers and refinancers.

The new report, released Tuesday by the Consumer Federation of America, found that inaccurate and incomplete information in consumers' credit files can depress their credit scores enough to raise their mortgage rate quotes dramatically.

"We conservatively estimate that 40 million consumers are at risk of being misclassified into the subprime market" because of errors or missing information in their credit files, said the report.

Conducted jointly with the National Credit Reporting Association, the study covered a sample of 502,623 merged credit files -- by far the largest independent statistical investigation of its type undertaken in the United States. Though credit scores are used by lenders nationwide to price mortgage applications, the new study reports that consumers' scores can vary widely, depending upon which of the three national credit repositories' information was used.

Individual credit scores are generated by running credit file histories through risk-prediction software installed at each of the private national repositories --

Equifax, Experian and TransUnion. Because the credit information in a consumer's file at each of the three is different, the credit scores generated from each repository often differ significantly. The new study found that 31 percent of all consumers' scores differed by 50 points or more depending on the repository used, and one out of 20 scores by 100 points or more.

In a hypothetical example, say your FICO credit score -- named for Fair, Isaac & Co., creator of the system -- is 710 at TransUnion. Yet on the same day your score at Experian is 670. And your Equifax score is even lower -- 660. According to the study, you have a 1-in-3 chance of experiencing a score variation like this of 50 points or more.

So what, you might ask? Plenty. That 50-point range could cost you a bundle of money, depending upon which score your lender uses. According to data compiled from about 5,000 lenders in a survey for Fair, Isaac, people with 710 FICO scores were quoted an average 6.01 percent rate for 30-year fixed-rate new loans last week. People with 660 FICOs were quoted an average 7.7 percent rate. On a $200,000 mortgage, that translates to $4,500 higher principal and interest payments per year -- all because of what the new study suggests may be incomplete or erroneous information in one or more of your credit files.

The study found that the average variation in scores for all consumers is 43 points, from high to low repository. The contents of consumers' files at the repositories vary because they exhibit "strikingly high levels" of factual errors and omissions, the report says. Banks, department stores, credit card companies and others who submit account-payment information to the repositories do so voluntarily. No federal law requires any lender or business to report your payment performance, good or bad. As a result, some creditors report data only to one or two of the repositories. Others report nothing.

Incomplete files are especially damaging to consumers when the missing information is positive and would tend to raise the scores. Hurt most of all, according to the study, are "consumers who are just beginning to establish credit" -- young adults, immigrants and others who are new to the financial system -- as well as those "who are working to re-establish their credit rating after bankruptcy."

Nearly 80 percent of all files examined in one phase of the investigation "were missing a revolving account in good standing." One of every three was missing a mortgage account that had never been late, and two out of three were missing installment accounts that had been paid on time.

Is there a problem here? You bet. Even the trade group that represents Equifax, Experian and TransUnion -- the Consumer Data Industry Association -- agreed in comments this week that the new study "has raised some legitimate questions about credit scoring" but said it needed to study the issue of credit file variations further. The association endorsed the study's main recommendations to consumers, including:

* Review all three of your credit reports at least once a year. Make sure nothing is in error or missing.

* Maintain consistency in identifying yourself in credit applications. Use your full legal name so you won't be confused with relatives whose credit records inadvertently could be mixed with your own.

* Demand detailed reasons from a lender who tells you your credit scores are low. Demand to know all the specific factors lowering your scores.

* When you discover errors or omissions, contact the repository involved to request corrections: Equifax (800-685-1111), Experian (888-397-3742) and TransUnion (800-888-4213).

Kenneth R. Harney's e-mail address is kharney@winstarmail.com.