On March 30 Sabrina and Michael, a couple from New York’s Nassau County, entered into a contract to buy their first home for $240,000 and put down $27,000 in escrow.

Michael, a 29-year-old real estate agent, said he was confident the couple would easily obtain a loan. Six months earlier they had been pre-approved for a mortgage on a house that was later pulled off the market.

But blemishes on his wife’s credit report, which she claims are mistakes, sank her Fair, Isaac score from 651 to 554.

Since then, the couple (who asked that their last name not be used) have been unable to obtain a loan approval. And the clock is ticking: They need to get a mortgage in less than three weeks, or they will lose the contract and at least $8,000 of the escrow.

Sabrina, 25, says she has resolved most of the problems with her credit reports, but updates take up to 90 days to be recorded.

The case underscores a downside to the mortgage underwriting process, which for years has been accelerating and now leaves little time to address problems that may arise. And it illustrates what some say is a growing problem as banks rely more on the evaluations of the automated underwriting systems of Fannie Mae and Freddie Mac — which are based in part on credit reports and Fair, Isaac scores — to make lending decisions.

Critics say that 60% to 80% of credit reports contain some incorrect data, which in some cases can produce inaccurate credit scores. Consumer activists and politicians argue that the practice of rushing applications through and not manually reviewing consumer credit reports is unfairly botching lending decisions and costing lenders business.

Michael says he sees the problem “all the time” in his job. The situation is getting worse, because the systems do not give potential borrowers an opportunity to look at their credit reports and address errors during the process, he said.

“There is no human being looking at the credit report,” he said. “The computer doesn’t know if there was an excuse or a letter to show that there was a problem with the information.”

The two underwriting systems, Fannie’s Desktop Underwriter and Freddie’s Loan Prospector, are used by lenders to make decisions about borrower eligibility for mortgage loans.

The lender enters the borrower’s application data into the system, which then collects and weighs information from credit repositories and other sources to determine the odds that the loan would be repaid. The odds are based on the way mortgages with similar borrower, property, and loan characteristics have performed in the past.

“It is critical that consumers have the opportunity to review or correct commonplace errors in our credit systems prior to or during an automated underwriting process,” said David Birenbaum, director of civil rights and fair housing for the National Community Reinvestment Coalition.

Credit industry officials said that errors can occur, but the problems are not widespread. When problems occur, consumers have immediate access to their credit reports and scores and can easily fix any mistakes, these officials say.

“We strive to make sure the information we have is the most accurate it can be,” said Clark Walter, a spokesman for Trans Union LLC. “We have a dispute resolution process; if somebody has something in their credit report that isn’t accurate, we are happy to work with them to see that it is resolved.”

Craig Watts, a spokesman for Fair, Isaac & Co., said the company’s scoring models are designed to be “very rich and very compensatory,” and produce accurate scores even when inaccurate data is included in the credit reports.

“The model is robust enough to handle inaccurate or missing information,” Mr. Watts said. “It is easy to throw stones at the system, but one shouldn’t lose sight of the fact that the American credit system is by far the strongest credit system in the world. No other credit system even comes close.”

Nonetheless, politicians and consumer activists are pushing legislation that would increase consumer access to their credit reports during the mortgage process.

Rep. Harold Ford Jr., D-Tenn., a member of the House Committee on Financial Services, introduced a bill on March 28 that would give consumers free access to their credit reports during all “creditworthiness decisions processes” — including those involved with mortgages. The bill also would toughen standards of accuracy within credit reporting practices.

Further, Richard Le Febvre, president of AAA American Credit Bureau of Flagstaff, Ariz., says that because the GSEs and lenders do not routinely review credit reports with borrowers during the underwriting process, they are violating the Fair Credit Reporting Act of 1970 and the Consumer Credit Reporting Reform Act of 1996.

“Consumers can’t fight what they can’t see, and it’s unfair if they can’t see credit report errors,” Mr. Le Febvre said. “Consumers are given the right to dispute and correct inaccuracies under both acts. Fannie and Freddie” and the lenders “are not allowing consumers their congressional rights.”

Spokeswomen for both Fannie and Freddie vigorously denied Le Febvre’s allegations.

“Fannie Mae encourages borrowers to obtain and review a copy of their credit report prior to beginning the mortgage loan application process,” a Fannie spokeswoman said. The government-sponsored enterprise provides potential borrowers with a list of credit bureaus for that information, she said.

A Freddie spokeswoman called the charges “absurd.”

Norm Magnuson, a spokesman for the Associated Credit Bureaus of America, a lobbying group for the credit industry, said the complaints of frequent errors on credit reporting are “simply not true.”

There have been “no scientifically based studies to indicate that consumer reporting files have a high proportion of errors,” he said. “I have yet to hear of or see any study that proves it.”

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