More than three in 10 U.S. homeowners have no idea what type of loan they own, according to a poll released by Bankrate.com Monday that suggested how confusion may be contributing to problems in the subprime mortgage sector.

Another troubling finding in the Bankrate.com survey was that 34 percent of homeowners who hold adjustable-rate mortgages (ARM) do not know what they will do when their loan resets to higher interest rates.

"Clearly, many homeowners are uninformed about their mortgages," said Greg McBride, senior financial analyst at Bankrate.com, a consumer financial data firm.

The U.S. home ownership rate rose to a record high in recent years as mortgage rates fell to the lowest level in decades. Low "teaser" ARM rates, aggressive marketing of exotic mortgages and loose underwriting standards by lenders allowed borrowers with spotty, or subprime, credit to buy homes as prices soared.

However, some subprime borrowers now are in danger of losing their homes because they cannot absorb the payment shock once the interest rates on their loans reset.

"Given that homeowners could be looking at an increase of several hundred dollars each month, this is a staggering statistic," McBride said in a statement.

The survey of about 1,000 adults nationally was conducted from March 16 through March 18.

The burden of growing monthly payments has already begun to take its toll, spurring worries among economists and in financial markets that the broader economy could be hurt.

The share of mortgaged homes at the start of the foreclosure process rose to a seasonally adjusted 0.54 percent in the fourth quarter of 2006, surpassing the previous record of 0.50 percent in the second quarter of 2002, according to the Mortgage Bankers Association.

The housing picture will likely turn gloomier. Foreclosures could rise by 33 percent this year from 2006's level, online real estate data provider RealtyTrac said Monday.

With mortgage rates holding steady, McBride suggested that it may be a good time for ARM holders to switch into fixed-rate loans to hedge against further rate increases.

"Now may be the time to lock into a mortgage with a fixed rate which remains near historic lows," he said.

Interest rates on a 30-year fixed-rate mortgage averaged 5.79 percent in the week ended March 16, versus the average 5.88 percent on a one-year adjustable-rate home loan, the MBA said last week.