Fannie Mae said American home prices will rise 6.1% this year, a pace the largest American mortgage financier called “unsustainable.”

The median American price for an existing single-family house probably will increase to $180,000 from $169,700 last year, Washington-based Fannie Mae said in a report. A month ago, the federally chartered mortgage company estimated a 5.3% gain in the median price, the point at which half of American homes sold for more and half for less.

Mortgage rates have fallen on signs job creation has slowed, said Fannie Mae’s chief economist, David Berson, in an interview. Lower rates make it possible for people to pay more for a home because their borrowing costs are less. The average American fixed rate likely will be 6% this year, Mr. Berson said. That would be the lowest in 38 years.

“Despite rapid price increases, most people have seen their monthly mortgage payment fall to the point that they are paying less now than they did five years ago,” Mr. Berson said.

The American median price for an existing home probably will be $186,700 in 2005, a 3.7% gain, as the average American fixed rate rises to 6.7%, Mr. Berson said. That growth pace would fall below the 4.4% historical average of the last 20 years, according to the National Association of Realtors. American home prices grew 7.6% in both 2003 and 2002, Mr. Berson said.

American home resales probably will reach 6.4 million this year, a gain of 4.8% from last year’s record 6.1 million transactions, Mr. Berson said. That’s higher than his month-ago forecast of 6.3 million sales.

In 2003, home sales gained 9.7% from the prior year’s 5.6 million as the average American rate for a 30-year fixed mortgage fell to 5.8%, the lowest annual average since 1965, according to data from Freddie Mac, Fannie Mae’s smaller rival.

Sales of new homes probably will reach 1.17 million, above last year’s record 1.09 million, Mr. Berson said. A month ago, he estimated there would be 1.14 million sales.

New home prices likely will gain 6.2% as the American median reaches $203,300, Mr. Berson said. New homes account for about 15% of American house sales.

Lending for mortgages to purchase homes probably will reach a record $1.27 trillion, a gain of 7.6% from last year, Mr. Berson said.

Refinancings likely will drop 57% to $1.14 trillion. Combined lending for both categories will be $2.42 trillion, down 37% from last year’s all-time high to the third-biggest volume on record, Mr. Berson said.