WASHINGTON — Fannie Mae and Freddie Mac have set terms for letting borrowers put down as little as 3 percent of a home’s cost to get mortgages, a step criticized by Republican lawmakers as a return to risky lending.

Starting Dec. 13, Fannie Mae will allow the lower down payments for first-time homebuyers and permit refinancing borrowers to reduce equity to 3 percent to cover closing costs, the company said Monday in a statement. Freddie Mac will begin a more limited program in March giving breaks to lower-income buyers and first-time borrowers who get housing counseling.

“These underwriting guidelines provide a responsible approach to improving access to credit while ensuring safe and sound lending practices,” Melvin Watt, who oversees the two U.S.-owned companies as head of the Federal Housing Finance Agency, said in a statement.

Watt encouraged the move as part of a broader effort to spur lending to minorities, young adults and first-time buyers. Lenders have tightened standards after paying tens of billions of dollars to settle lawsuits over mortgage-underwriting flaws.

Fannie Mae and Freddie Mac, which buy more than half of new home loans and package them into bonds, allow down payments as low as 5 percent. Fannie Mae accepted 3 percent down as recently as November 2013 before increasing the requirement in a tightening of its underwriting standards.

The move to allow lower down payments has generated criticism from some Republicans and industry officials. Rep. Jeb Hensarling of Texas, the chairman of the House Financial Services Committee, has faulted the idea as a return to the policies that caused the housing crash.

Officials of Fannie Mae and Freddie Mac said rules banning risky loan features will ensure that the new low-down payment mortgages are safe. Only borrowers buying or refinancing a single-family primary residence will be eligible.