The Consumer Financial Protection Bureau is wrestling with its most important mortgage rule to date – one that will impact hundreds of thousands of families struggling in a difficult mortgage market.

Given the widespread implications of this rule, it's not surprising that, amidst so much speculation, the bureau is taking some time to get it done. The bottom line is: The CFPB has to get this right.

How difficult is the market for mortgage credit today? Federal Reserve Chairman Ben Bernanke said it best in a speech to Operation Hope on November 15: "Tightening of credit standards was an appropriate response to the lax lending conditions … However, it seems likely at this point that the pendulum has swung too far the other way, and that overly tight lending standards may now be preventing creditworthy borrowers from buying homes, thereby slowing the revival in housing and impeding the economic recovery." 

I agree, and the stakes couldn't be higher.

As required by the Dodd-Frank Act, the mortgage rule in question will provide lenders with a way to demonstrate a borrower's "ability to repay" a loan. In order to be approved, applicants must meet the requirements of a "qualified mortgage," defined by the CFPB. Those who don't meet this set QM standard will likely be unable to get mortgage credit.

Adding to the complexity of the rulemaking, the CFPB must determine what legal standards will apply to loans that adhere to the QM standard. Lenders must have a safe harbor with clear, well-defined standards. Without it, they face the threat of costly litigation and will be reluctant to offer mortgages to anyone other than those with the highest incomes and credit scores, regardless of how broadly the qualified mortgage might be defined.

What should this suggest to the CFPB?  First, the QM definition should include, at a minimum, all of the mortgages being underwritten in the overly tight credit environment Bernanke's statement acknowledges.  Second, lenders should be protected from claims when they scrupulously adhere to loan terms under the QM definition that the CFPB is writing.

In recent weeks, there have been suggestions that the CFPB might be considering splitting the baby and providing a safe harbor for some QM loans, which they would consider to be mainstream loans, but only a flimsy rebuttable presumption for other high quality loans. That will only swing the pendulum further in the wrong direction.

The CFPB should be working to craft the best QM rule possible to determine what borrowers meet the ability to repay test, not working to further stratify the rule in a way that will make it needlessly more difficult – and more costly – for creditworthy borrowers to get loans.

That could put homeownership out of reach for thousands of hard-working, creditworthy Americans and bring the housing recovery to an abrupt halt. That's not something our economy, which already faces daunting "fiscal cliff" challenges, can afford.

Frank Keating is president and CEO of the American Bankers Association and former two-term governor of Oklahoma.