Rates on 30-year mortgages fell this week to the lowest level in six weeks.

The mortgage company Freddie Mac reported on Thursday that 30-year, fixed-rate mortgages averaged 6.22 percent this week, compared with 6.30 percent last week.

The decline was only the second since early December. It pushed rates to the lowest level since the 30-year mortgage was at 6.21 percent the week of Jan. 11.

Analysts said the drop reflected in part weakness in the housing industry, shown by a 14.3 percent plunge in construction of new homes and apartments in January. That decline pushed the seasonally adjusted annual rate of home building down to 1.408 million units last month, the slowest pace in nearly a decade.

"Market participants were concerned over how much drag the slowing housing market may have on economic growth," said Frank Nothaft, Freddie Mac's chief economist.

Freddie Mac's survey showed that other types of mortgage rates also fell this week.

Rates on 15-year, fixed-rate mortgages, a popular choice for refinancing, were at 5.97 percent, down from 6.03 percent last week.

Five-year adjustable rate mortgages slipped to 5.96 percent from 6.01 percent last week.

One-year ARMs dropped to 5.49 percent from 5.52 percent last week.

The mortgage rates do not include add-on fees known as points. Thirty-year, 15-year and five-year mortgages all carried a nationwide average fee of 0.5 point. One-year mortgages carried an average fee of 0.7 point.

A year ago, rates on 30-year mortgages stood at 6.26 percent while 15-year mortgages were at 5.89 percent, five-year adjustable rate mortgages averaged 5.96 percent and one-year ARMs were at 5.32 percent.

TRENDS . . .RealSpring 2007, a symposium for real estate agents and brokers, will focus on the fluid dynamics shaping the residential real estate market in the District going into the spring sales season, providing information on changing design trends and economic forecasts.

The participants will include Neil O. Albert, deputy mayor for planning and economic development; Steve Moore, president of the Washington DC Economic Partnership; and Anna Simone, an interior designer who appears on HGTV's "Design Interns."

The symposium will start at 10:30 a.m. Wednesday, Feb. 28, at the Carnegie Institution, 1530 P St. NW.

It is being presented by Metropolis Development Co. and the Washington DC Economic Partnership. Sponsors include Bank of America; MetroWeekly; Regional Title; Vida, Beers & Cutler; and Ober Kaler.

For details, visit http://www.realspring2007.com.

Send realty announcements by e-mail to realestate@washpost.com.