By Nick Timiraos 

Wells Fargo will lower its minimum credit score for certain mortgages eligible for government backing, a sign that mortgage lending standards may be starting to slowly thaw.

Franklin Codel, a top mortgage executive at the bank, announced at a real-estate industry conference last week that the bank would begin originating purchase loans backed by the Federal Housing Administration with credit scores as low as 600, down from its previous limit of 640, through its retail channel.

"The goal is to increase access to credit, especially for low- and moderate- income borrowers and first-time home buyers," said Tom Goyda, a bank spokesman. "These are fully underwritten, fully documented loans, consistent with FHA program guidelines and responsible lending principles."

The FHA doesn't make loans but it insures those that meet certain standards. It requires down payments of at least 3.5% for loans with credit scores as low as 580, and it requires down payments of 10% for loans with credit scores below 580.

The policy change could lead other lenders to gradually relax standards that were sharply tightened after the housing bust in 2008, said industry executives. Wells Fargo is the nation's largest mortgage lender and funded more than $356 billion in originations last year, or around 19% of all mortgages, according to Inside Mortgage Finance, an industry newsletter.

Borrowers with credit scores below 620 have traditionally been considered "subprime" borrowers. While the FHA has traditionally served borrowers with weaker credit, it stood mostly on the sidelines during the subprime mortgage bubble because its income-verification standards, among other rules, were considered too stringent. The agency's market share tumbled until the subprime market disintegrated in 2007, after which it returned as a major player.

Industry analysts have said that lenders are likely to slowly ease credit standards this year because home prices have stabilized and refinancing volumes have dropped, leaving banks on the prowl for new business. "With volume going down, everyone is looking to tweak, if not loosen, the underwriting in certain areas," said Guy Cecala, publisher of Inside Mortgage Finance.

Still, banks face new regulations over mortgage underwriting this year, and few expect a return to the go-go days of the subprime boom that began in the early 2000s. Credit loosening "is going to be slow, and it's going to be piece-by-piece," said Mr. Cecala.

Officials in the Obama administration and at the Federal Reserve have repeatedly raised concerns over the past year that mortgage-lending standards, after being too lax during last decade's housing bubble, have grown too stringent. Those comments appear designed to jawbone the industry into removing so-called "credit overlays," or additional underwriting rules that are stricter than the minimum standards of the FHA or loan giants Fannie Mae and Freddie Mac.

In a bid to further encourage such easing, the FHA last year began allowing borrowers who have gone through a foreclosure or bankruptcy but who have repaired their credit to become eligible for a new loan after waiting as little as one year. Previously, they had to wait at least three years.

Since the crisis hit, banks have been reluctant to make FHA loans to borrowers with credit scores below 620 because of concerns that they could be forced to buy back those loans or face other sanctions if they have default rates that are above the industry's average.

Wells executives have said that they were willing to ease standards modestly because they are more confident that forthcoming policies surrounding defaulted loan repurchases will provide more clarity, according to people familiar with the matter. Wells could undo its recent easing, these people said, if it isn't comfortable with those rules when they are finalized.

Mr. Goyda said that the bank will evaluate any new lending and "continue to see whether it's appropriate to make changes in the future."

This isn't the first time that Wells has experimented with easing standards on FHA-backed loans. In 2011, the bank said it would began accepting applications with credit scores as low as 500. The cutoff was later increased to 600 and then to 640. "What we found over almost a year...was a very, very tiny percentage of those borrowers were being approved, and fewer of those were ultimately funded," said Mr. Goyda.

Separately, Wells was hit with a federal lawsuit in 2012 that accused the bank of "reckless" lending through the FHA program. The bank has said it acted in good faith and it is fighting the lawsuit in federal court in Manhattan.

Economists said Wells Fargo's change isn't likely to lead to a big boost in lending immediately. "It is going to take some time for that news to get out to the potential buyer--that now there might be an ability to qualify whereas a year or two ago, that wasn't the case," said Michael Fratantoni, chief economist for the Mortgage Bankers Association. "I don't see a flood of applicants coming in."

Average credit scores on FHA loans for home purchases stood at around 690 in December, down from 700 in 2012, according to Ellie Mae, a mortgage-software firm. Under a system devised by Fair Isaac Corp., credit scores range from 300 to 850.

Write to Nick Timiraos at nick.timiraos@wsj.com