U.S. mortgage rates fell in the past week to the latest in a series of record lows amid concerns about the state of the U.S. economy, according to a survey released on Thursday by Freddie Mac, the second-largest U.S. mortgage finance company.

Rock-bottom rates should continue to spur demand for home loan refinancing, putting extra cash into consumers' hands that they can save, use to pay off existing debt or funnel into the economy through extra spending.

Interest rates on U.S. 30-year fixed-rate mortgages, the most widely used loan, averaged 4.42 percent for the week ended August 19, down from the previous week's 4.44 percent and its year-ago level of 5.12 percent, according to the survey.

Thirty-year mortgage rates have fallen to fresh lows for nine straight weeks. Freddie Mac started the survey in April 1971.

Meanwhile, 15-year fixed-rate mortgages averaged 3.90 percent, down from 3.92 percent last week, the lowest level since Freddie Mac began surveying this loan type in 1991. Fifteen-year mortgage rates have hit fresh lows for six straight weeks.

Investors in long-term bonds appear very confident that inflation will remain in check, and as a result long-term fixed mortgage rates have continued to fall, Amy Crews Cutts, Freddie Mac deputy chief economist, said in a statement.

Mortgage rates are linked to yields on Treasuries and yields on mortgage-backed securities.

The Federal Reserve last week said it will be using proceeds from maturing bonds in its mortgage portfolio to buy more Treasury debt.

Low mortgage rates offer a glimmer of hope for a housing market, which has been struggling to gain traction since the expiration of popular home-buyer tax credits.

To take advantage of the tax credits, buyers had to sign purchase contracts by April 30. Contracts originally had to close by June 30, but that has been extended by three months.

By lowering monthly mortgage payments, lower rates may also help some homeowners avoid default and foreclosure if their credit is good enough.

LOW RATES, HIGHER DEMAND

Bob Walters, chief economist at Quicken Loans in Detroit, Michigan, said home loan demand at his company has jumped 50 percent over the past month.

Nearly every person who has a mortgage right now can benefit from refinancing, he said. The problem is, many of them cannot due to an array of factors.

Lending standards are tight and some homeowners are underwater with their mortgages, he said.

Underwater mortgages are one of the biggest banes to homeowners because negative equity -- where the outstanding balance of a loan is greater than the value of a home -- makes many of them unqualified for refinancing and prevents some from selling.

Borrowers in negative equity positions are more prone to defaults and foreclosures, both of which are already at sky-high levels.

Unemployment is another big factor in the inability of some homeowners to refinance, he said. The U.S. Labor Department said on Thursday new U.S. claims for unemployment benefits rose to the highest level since mid-November.

The Mortgage Bankers Association said on Wednesday U.S. mortgage applications leaped last week as rock-bottom interest rates lifted demand for home refinancing to the highest level in 15 months, a development that could portend stronger economic growth.

Freddie Mac said rates on 5/1 ARMs, set at a fixed rate for five years and adjustable in each following year, was 3.56 percent, unchanged from last week, remaining at its lowest level since Freddie Mac began tracking this loan type in 2005.

One-year adjustable-rate mortgages (ARMs) were 3.53 percent, unchanged from last week.

A year ago, 15-year mortgages averaged 4.56 percent, the one-year ARM was 4.69 percent and the 5/1 ARM 4.57 percent.

(Editing by Todd Eastham)

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