Credit bureaus sometimes provide Americans with credit scores that are different from those that lenders use in deciding whether to offer a loan and at what interest rate, the government’s consumer watchdog found in a study released Tuesday.

Researchers at the Consumer Financial Protection Bureau found that the discrepancy happens for as many as one in four people.

The consumer agency issued the study five days before it will begin supervising credit-reporting firms. That will give the bureau oversight of about 30 companies that make up the majority of the $4 billion industry.

Credit agencies have come under greater scrutiny as consumer advocates question the accuracy of the scores, which affect the ability to get a mortgage, car loan, credit card and sometimes even a job. The scores aim to measure the likelihood that a consumer would repay a debt based on his or her record.

Given the widespread use of the scores, even small variations can have huge consequences. Discrepancies could lead some lenders to deny applicants student loans or mortgages, or offer terms that are worse than warranted, the study concluded.

“When consumers buy a credit score, they should be aware that a lender may be using a very different score in making a credit decision,” Richard Cordray, the CFPB’s director, said in a statement. The study was based on a random sample of 200,000 credit files from the three major credit reporting agencies — Experian, TransUnion and Equifax.

Consumer advocates said borrowers are unlikely to know about any discrepancy in their credit scores, although reporting firms should make them aware.

“The report illustrates how opaque the process is in determining credit scores,” said Bill Sermons, director of research at the Center for Responsible Lending. “The deck is stacked against consumers because they don’t know what information is being used to determine how much they pay for credit.”

The advocates called on Congress to grant Americans free access to the score most widely used by lenders, FICO. In some cases, consumers are provided scores different from the FICO measure.

If they ask, consumers can pay to see their FICO scores from TransUnion and Equifax. Experian does not make the FICO score available.

“It’s like a student applying to college and not knowing whether the school uses an SAT vs. an ACT score. And the student doesn’t even have the right to find out what his or her ACT score is,” said Persis Yu, a lawyer with the National Consumer Law Center.

The consumer bureau recommends shopping around for the best loan terms. Even if lenders are provided the same score, their terms may vary based on individual risk assessment and competitive pressure, the report said.

Speaking on behalf of the three major credit firms, Stuart Pratt, chief executive of the Consumer Data Industry Association, said that consumers should also ask questions about the credit scoring model used when purchasing reports.

“The credit score is a valuable educational tool and can enable consumers to better understand their creditworthiness relative to other consumers,” he said.

Pratt said the CFPB’s study confirmed the value of the scores. “The study sheds new light on why consumers can trust the credit score disclosures they receive and the products in the commercial marketplace,” he said.