This year's subprime-mortgage turmoil has forced a Philadelphia specialty-finance company to record an unrealized loss of $65.6 million on its $3.6 billion portfolio of mortgage-backed securities.

While Alesco Financial Inc. executives told investors yesterday that the impairment was expected to be temporary, and an analyst said that it was smaller than anticipated, the loss illustrates how the recent spike in subprime-mortgage defaults has rippled through the securities markets.

The loss, reported for the quarter ended March 31, reflects a decline in the market value of the mortgage-backed securities, not defaults on specific mortgages. Alesco said that $15.8 million in bonds were likely to be downgraded by Moody's, but were not expected to lose their investment grade.

As the subprime-mortgage crisis unfolded on Wall Street, Alesco's shares fell as much as 32 percent, from a high of $11.75 in late January to a low of $8.04 about a month ago. The shares closed yesterday at $9.32, up 12 cents, on the New York Stock Exchange.

On the heels of the nation's subprime-mortgage problems, Alesco is considering a major change in strategy: converting from a real estate investment trust to a publicly traded partnership.

As a real estate investment trust, 75 percent of Alesco's income must come from real estate. Unlike many real estate investment trusts, Alesco invests in real estate securities, such has home mortgages, rather than actual property.

"By changing our corporate structure, we may be able to reduce our need for many of our mortgage assets" and shift investments into assets with higher returns, company chairman Daniel G. Cohen said.

Marvin Loh, a research analyst with Oppenheimer & Co. Inc., said "subprime has changed the dynamic" of the mortgage-backed securities market and "definitely had an impact on the decision" by Alesco to explore the conversion into a partnership.