Historically low interest rates for 30-year mortgages edged down another tick, Freddie Mac said in its most recent survey, which showed lenders across the country offering the benchmark loan at 3.78 percent compared to 3.79 percent the week prior. The typical rate on a 15-year fixed loan remained steady at 3.04 percent

According to another survey, new home sales are rising, with the low rates helping to make housing more affordable

But many homeowners are trapped in homes worth less than their mortgages, constraining home resales and holding back the recovery of the housing market

Reflecting the bargain home-loan rates, the Mortgage Bankers Association recently increased its mortgage origination forecast for 2012 by almost $200 billion, but attributed the greater volume entirely to an increase in borrowers refinancing existing loans

According to the trade group, they now expect $1.28 trillion in mortgages to be written in 2012, which is up from $1.26 trillion in 2011. Refinance transactions are expected to total $870 billion, about the same as last year, while the forecast indicated that purchase loans would decrease from $415 billion to $409 billion

Economist for the Mortgage Bankers Association, Mike Fratantoni said that market turmoil in Europe and slower economic growth throughout the world is continuing to depress the yield on the 10-year U.S. Treasury note, which serves as a benchmark for fixed-rate mortgages

We are projecting lower U.S. mortgage rates for the rest of 2012 and raising our refinance forecast as a result, Fratantoni said

The survey by Freddie Mac, the huge government-supported loan buyer, asks lenders what terms they are offering to borrowers with good credit and down payments of 20 percent for home purchases or at least 20 percent home equity if they are refinancing

Freddie Mac said that in the last week of May, the average start rate for a one-year adjustable-rate loan averaged 2.75 percent, down from 2.78 percent the week before. For “hybrid” loans that become adjustable after five years at a fixed rate, the typical start rate remained unchanged at 2.83 percent in the last week in May

The Freddie Mac survey assumes that borrowers pay relatively little in points and upfront fees to the lenders. According to the survey, borrowers would have paid on average 0.8 percent of the loan amount for the 30-year fixed loan, 0.7 percent for the 15-year fixed loan, 0.6 percent for the 5-year hybrid mortgage, and 0.4 percent for the home loan that adjusts annually

By paying additional discount points to lenders, borrowers can “buy down” mortgage rates. They also often pay additional closing costs not included in the Freddie Mac survey.