With U.S. lawmakers heading toward the edge of the “fiscal cliff,” government-backed mortgage bonds that fund the vast majority of home loans are looking like a safe haven for investors, helping push mortgage rates to new lows.

Rates on 30-year fixed-rate mortgages averaged 3.34 percent with an average 0.7 point for the week ending Nov. 15, down from 3.4 percent last week and 4 percent a year ago, Freddie Mac said in releasing the results of its weekly Primary Mortgage Market Survey.

That’s a new low in Freddie Mac records dating to 1971. In the four decades that Freddie Mac has conducted the mortgage market survey, rates on 30-year fixed-rate loans had never been below 4 percent until last year.

The survey showed rates on 15-year fixed-rate mortgages averaging 2.65 percent with an average 0.7 point, down from 2.69 percent last week and 3.31 percent a year ago. That’s also a new record in Freddie Mac records dating to 1991.

For five-year Treasury-indexed hybrid adjustable-rate mortgage (ARM) loans, rates averaged 2.74 percent with an average 0.6 point, up from 2.73 percent last week but down from 2.97 percent a year ago. Rates on five-year ARM loans hit a low in records dating to 2005 of 2.69 percent during the week ending July 19.

Rates on one-year Treasury-indexed ARM loans averaged 2.55 percent with an average 0.3 point, down from 2.59 percent last week and 2.98 percent a year ago. That’s a new low in records dating to 1984.

Applications for mortgage loan applications bounced back last week after being dented by Hurricane Sandy, according to a separate survey by the Mortgage Bankers Association.

That survey showed applications for purchase mortgages were up a seasonally adjusted 11 percent during the week ending Nov. 9 compared to the week before, and up 22 percent from a year ago.

Bond prices and yields move in opposite directions, and increased demand for mortgage-backed securities (MBS) guaranteed by Freddie Mac, Fannie Mae and Ginnie Mae has pushed mortgage rates down.

The Federal Reserve has been one of the biggest purchasers of MBS, in a deliberate move to stimulate the economy by lowering the cost of borrowing.  A first round of “quantitative easing” by the Fed that wrapped up in 2010 helped push mortgage rates below 5 percent. That program involved the purchase of $1.25 trillion in Fannie and Freddie MBS and debt.

A third round of quantitative easing (“QE3”) announced by the Fed on Sept. 13 has boosted its MBS purchases by $40 billion a month. Because of the sluggish pace of the recovery, Fannie Mae economists think that open-ended program could last through all of 2013 and perhaps into 2014, and grow the Fed’s balance sheet by $1 trillion.