About 1.3 million homes nationwide received foreclosure-related warnings last year, up from 717,522 in 2006, Irvine-based RealtyTrac said. Foreclosure filings rose 75 percent from the previous year to 2.2 million.

More than 1 percent of all U.S. households were in some phase of the foreclosure process last year, up from about half a percent in 2006, RealtyTrac said.

Besides Nevada, Florida, Michigan and California posted the highest foreclosure rates, the company said.

The filings included notices warning owners that they were in default or that their home was slated for auction or for repossession by a bank. Some properties may have received more than one notice if the owners had multiple mortgages.

A late-year surge in the number of properties reporting foreclosure filings suggests that many are in the initial stages of the foreclosure process and could end up lost to foreclosure this year unless lenders or the government steps in, RealtyTrac said.

"It does appear that we're seeing a new batch of properties enter the process," said Rick Sharga, RealtyTrac's vice president of marketing.

RealtyTrac is forecasting that the pace of foreclosure filings will remain steady, rather than accelerate during the first half of 2008.

"Assuming nothing else bad happens economically ... we will have exhausted the bulk of the worst-performing loans by the end of June," Sharga said, referring to adjustable-rate mortgage loans made to borrowers with poor credit.

Many of these subprime loans defaulted last year, triggering a credit crisis and saddling major financial institutions with losses.

More than 1.8 million subprime mortgages are scheduled to reset to higher interest rates this year and next.

Last year's explosion in foreclosure activity came amid a worsening housing downturn, as falling home values ate into homeowners' equity, making it harder for many to refinance into more affordable loans or to find buyers. Those options had helped keep troubled homeowners from sliding into foreclosure.

"We went from a sort of buying frenzy to a foreclosure frenzy in the last two years," Sharga said.

Recent efforts by government and mortgage lenders to help homeowners at risk of falling seriously behind on mortgage payments have had a marginal impact on the U.S. foreclosure rate so far, Sharga added.

In December alone, foreclosure filings soared 97 percent from the same month a year earlier to 215,749. It was the fifth consecutive month in which foreclosure filings topped more than 200,000, RealtyTrac said.

In the fourth quarter, filings rose 86 percent from the prior-year quarter but only 1 percent from the third quarter.

Florida had more than 2 percent of its properties in some stage of foreclosure last year. The state reported 279,325 filings on 165,291 homes, more than twice the previous year's total.

In Michigan, where job losses are pressuring many homeowners, 1.9 percent of all households received a foreclosure filing last year. In all, 136,205 filings were issued on 87,210 properties, up 68 percent versus filings in 2006.

California led the nation in total foreclosure filings and the number of homes in some stage of foreclosure last year.

A total of 481,392 filings were issued on 249,513 properties, more than triple the number of filings in 2006, RealtyTrac said.

In all, 1.9 percent of households in California received foreclosure filings. Many of the homes receiving foreclosure filings in the state were in the inland markets, where new construction and more affordable prices helped fuel a spike in sales toward the end of the housing boom.

Other states in the 2007 foreclusure top 10 were Colorado, Ohio, Georgia, Arizona, Illinois and Indiana.