Wells Fargo, the largest U.S. home lender, has assigned about 400 underwriters to originate mortgages for the bank to hold, with as many as 40 percent of those loans likely to fall outside government guidelines taking effect this week.

The bank is training the group as a way to increase lending without losing control of quality, according to Brad Blackwell, head of portfolio lending for the San Francisco-based lender. The group will review loans including those with terms that prevent them from qualifying for protections provided by the Consumer Financial Protection Bureau, or CFPB, under new rules, he said.