Thirty-year, fixed-rate mortgages could be harder to find as Fannie Mae and Freddie Mac wind down, potentially forcing more borrowers to turn to short-term mortgages and variable interest rate loans, according to local community banks and credit unions.

Earlier this month, the Treasury Department announced that it would require Fannie Mae and Freddie Mac, the two government-sponsored entities that back much of the nation’s mortgages, to whittle down the number of mortgages they hold by 15 percent every year.

Community banks and credit unions could be hit the hardest, because large banks can package mortgages as securities and sell them off to raise more money to lend.

“The vast majority of the mortgages that we provide are 30-year, fixed-rate mortgages that we sell through partnerships to Fannie and Freddie,” said Juli Anne Callis, president and chief executive of the National Institutes of Health Federal Credit Union in Rockville. “Without them, we would have $15 million to $20 million in mortgage needs that we could not fulfill ever month.”

“Frankly, anything that’s 20 years or longer, we wouldn’t be able to keep on the books in this low-rate environment,” she added.

It is still not clear exactly how the wind downs will occur. Both Democrats and Republicans agree that the entities need to be phased out eventually, but have different takes on exactly when and how that should happen.

“Right now we’re still in a broad theoretical stage with this stuff,” said Joe Pigg, senior counsel at American Bankers Association. “Even though the Treasury calls this an accelerated winding down, Fannie and Freddie can’t be wound down until Congress acts and puts something else in their place.”

Even so, area banks say they are already looking into private investors to take the place of the mortgage finance giants.

“Fannie and Freddie have been very strong partners for us,” said Lynne Pulford, manager of the mortgage division at Sandy Spring Bank in Olney. “We’re looking for private investors to fill that void if they were in fact to go away.”

Other institutions, such as the NIH Federal Credit Union, said they likely would have to turn to shorter-term loans, like five- and seven-year mortgages, and cut back on fixed-rate offerings.

“For members, it would mean a situation where they’d have to buy variable rate mortgages,” Callis said. “They’re not awful, but you can bet they’ll go up, considering how low rates are now.”

The Federal Reserve has kept the interest rates for bank-to-bank lending near zero since December 2008, and has said that it will continue to do so at least until the end of 2014.

“The 30-year, fixed-rate loan is a very popular product,” said Pigg, the bankers association counsel. “I think whatever system we evolve to would have to find a way to meet market demand and continue to serve those loans.”

Some area banks, though, said they won’t be affected — at least not directly. National Capital Bank in Southeast Washington has never bundled its mortgage loans and sold them in secondary markets, according to Jim Didden, the bank’s president.

Instead, the bank, which was founded in 1889, backs all loans itself and keeps mortgages on its books.

“It’s the traditional way banks did business,” Didden said. “We keep the option open in case we want to sell some of these 30-year loans in the future. But for now, we make good loans that we’re comfortable with — and so far it’s served us well.”