NEW YORK — Anita Britten refinanced her two-story brick cottage in Lithonia, Ga., in 2003 using a hybrid adjustable rate mortgage, or ARM.

Her lender reassured her that she could refinance out of the riskier loan into a traditional one when her interest rate started to reset.

Three years later, Britten can't get a new mortgage and her monthly payment has jumped by a third in six months. She can't afford her payments and may face foreclosure if her financial situation doesn't change.

As more ARMs adjust upward and housing prices begin to dip, many Americans like Britten can't refinance and are finding themselves trapped in too-high monthly payments. For those who can't make their payments, foreclosure — the legal process by which the lender repossesses the house because the owner has defaulted on payments — is the only way out.

Figures just released by the Mortgage Bankers Association show that foreclosure activity fell in the first quarter of 2006 over the first quarter of 2005 for all loan categories except subprime loans. The MBA didn't specify how many of subprime loans were adjustable rate mortgages.

But while a strong economy helped hold down the foreclosure rate in the first quarter, homeowners and experts fear the market has turned and numbers are headed upward.

Last year, foreclosures hit a historical low nationwide at about 50,000. But that number has more than doubled since then, according to Foreclosure .com.

And delinquency rates appear to be rising, as well. While delinquency rates fell for most types of loans from the fourth quarter of 2005 because of a stronger economy, delinquencies for both prime and subprime ARM loans increased year-over-year in the first quarter, according to the MBA.

In the past several years, millions of Americans took equity out of their houses and refinanced when interest rates were at historical lows and housing prices were at record highs.

Many of them chose to refinance into hybrid ARMs that lenders were aggressively pushing. ARMs, which featured a low introductory interest rate that resets upward after a set period of time, were easier to qualify for than traditional fixed-rate loans.

ARMs are now starting to fall by the wayside as the difference in interest rates narrows. The average rate on a 30-year fixed rate loan in May was 6.60 percent compared with 5.63 percent on a one-year ARM, according to Freddie Mac. In 2003, rates on a 30-year fixed were at 6.54 percent, while ARMs carried a 3.76 percent rate.

This year, more than $300 billion worth of hybrid ARMs will readjust for the first time. That number will jump to approximately $1 trillion in 2007, according to the MBA.

Monthly payments will leap too, many beyond what homeowners can afford.