Homeowners could soon have an easier time selling their homes for less than what they owe on their mortgages, under new guidelines from a federal housing regulator and mortgage-finance giants Fannie Mae and Freddie Mac. The Federal Housing Finance Agency on Tuesday announced measures to make “short sales” of underwater homes easier for homeowners, including extending help to people who have financial difficulties but haven’t missed mortgage payments. One part of the plan is for Fannie and Freddie to place a $6,000 cap on the amount of money holders of second mortgages can receive when the sale is completed, as a way to prevent the mortgage holders from haggling over their slice of the home-sale proceeds.