In a move aimed at making it easier for consumers to get mortgages, the federal regulator for Fannie Mae and Freddie Mac FMCC -2.12% said Monday the mortgage giants would address a big controversy of the housing bust: who gets stuck with bad loans.

Fannie and Freddie have forced banks to repurchase billions of mortgages that have defaulted over the past few years. To protect themselves from facing similar demands, banks have raised their lending standards beyond what the two mortgage companies require, scrutinized appraisals, and demanded extensive documentation of a borrower’s income and assets.

To ease lenders’ concerns, the Federal Housing Finance Agency said on Monday it would issue guidance that would detail steps that could limit their risk of having to buy back defaulted mortgages in costly loan “put-backs.”

For example, banks will be released from having to buy back a loan under certain conditions if the mortgage has a record of on-time payments for the first 36 months, or for the first 12 months on loans that are part of an existing refinancing initiative. Those changes will take effect next year.

It isn’t clear how far the latest guidance will go toward making it easier for consumers to get a mortgage. While mortgage rates have fallen by a full percentage point over the last 18 months, demand for new loans remains nearly unchanged from one year ago.

“For the market to reclaim the strength it once had—and to provide a cornerstone for the mortgage market of the future—it is vital we consider ways to improve” the loan review process, Edward DeMarco, the acting director of the Federal Housing Finance Agency, told an industry conference Monday.

Fannie and Freddie don’t make loans, but instead acquire or guarantee those made by banks and other lenders. Those banks make certain “representations and warranties” to Fannie and Freddie when they sell loans, and the mortgage giants can force banks to take back any loans found to run afoul of those standards. Over the past year, banks have charged that Fannie and Freddie are putting back more loans that defaulted for reasons that had nothing to do with an underwriting defect.

Fannie and Freddie have asked that banks buy back nearly $75 billion in loans that lenders sold to the mortgage giants since 2005, according to Inside Mortgage Finance, an industry newsletter.

The new rules won’t have any impact on the current battle over who winds up with the bad loans made during the boom years.

In exchange for shielding banks against put-backs on certain loans, Fannie and Freddie will step up screening for potential loan defects of new mortgages. Officials said Monday that a more robust data-collection system implemented in recent years has made it possible to increasingly review loans as they are acquired, as opposed to reviewing them after they default.

Because buying back one bad loan can wipe out the profit on 30 or 40 good loans, lenders have become extremely cautious in approving mortgages. “If there’s a question at some point, it’s the safer move to deny” the loan, said Bob Walters, chief economist at Quicken Loans.

An April survey of senior loan officers by the Federal Reserve showed that the risk of put-backs had become a leading factor preventing banks from easing credit standards for mortgages, even as they have eased standards for other loans, such as cars and credit cards.

“Lenders have pulled back because they don’t know what their future exposure around repurchases is going to be…. Ultimately that has limited the availability of mortgage credit,” said Maria Fernandez, associate director for housing and regulatory policy at the FHFA.

The agency’s goal, she added, “is to be very clear with lenders what our expectations are so we can help facilitate more liquidity.”

Industry analysts said the impact of the new rules would rest largely on the details of the rules issued by Fannie and Freddie, and how they enforce those rules. “If you have written guidance from these quasi-government agencies what their terms are, they can’t really walk away from that,” said Laurence Platt, a banking-industry lawyer at K&L Gates in Washington.

At the same time, banks face new regulation in the coming year that could keep them in a defensive position. One provision of the Dodd-Frank financial-overhaul law, for example, carries potentially steep penalties if banks don’t properly ensure a borrower has the capacity to repay a loan.

Some large banks are also facing subpoenas from federal prosecutors as part of an effort by the FHFA’s inspector general to determine whether the U.S. could recoup money from banks that sold defaulted loans to Fannie and Freddie, according to people familiar with the investigation.

“It’s one step forward, two steps back,” said Mr. Platt. “You have a bunch of different legs that aren’t walking in unison.”

By NICK TIMIRAOS

COURTESY OF YOUR NUMBER ONE ARCADIA REAL ESTATE AGENT